Osama bin Laden was buried at sea Monday after U.S. forces raided his well-appointed hideout in Pakistan, shot him in a firefight in which at least one of his wives was used as a human shield, then spirited his body out of the country aboard a helicopter, U.S. officials said.

In a White House briefing Monday afternoon, John O. Brennan, President Obama’s chief counterterrorism adviser, said it was “inconceivable that bin Laden did not have a support system” in Pakistan that allowed him to live comfortably with his family in a town north of the capital. He said U.S. officials are pursuing this with the Pakistanis, who were pointedly not informed about the raid before it took place.

Obama made one of the “gutsiest calls” of any president in deciding to go ahead with the raid based on his confidence — but only circumstantial evidence — that bin Laden was indeed living in the compound in Abbottabad, Pakistan, Brennan said. He said there were “absolutely” disagreements among Obama’s advisers about that course of action.

Brennan described tense moments in the White House Situation Room on Sunday as Obama and his top aides monitored the raid “in real time” and “the minutes passed like days.” When it became clear later that bin Laden was dead, he said, the president’s reaction was, “We got him.”

The death of the long-hunted al-Qaeda leader, who had eluded intensive U.S. efforts to capture or kill him after the Sept. 11, 2001, terrorist attacks he ordered, triggered warnings Monday that his radical Islamist network or sympathizers could try to retaliate against Americans or U.S. interests.

It also served, U.S. officials said, to send a message to the extremist Taliban movement fighting to make a comeback in Afghanistan, where it had harbored bin Laden and al-Qaeda before being driven from power by U.S.-backed Afghan forces in November 2001. The message: Give up hope of defeating U.S. and NATO forces, renounce al-Qaeda and join the political process.

Bin Laden was killed early Monday in Pakistan (Sunday afternoon in Washington) in what officials described as a surgical raid by U.S. Special Operations Forces on his compound in Abbottabad, a garrison town 72 miles by road north of the capital, Islamabad. The raiding team reportedly was led by U.S. Navy SEALs.

Also killed in the raid were bin Laden’s son Khaled, two brothers who were harboring him and one of his wives, officials said.

In a rare Sunday night address from the East Room of the White House, President Obama said a small team of U.S. personnel attacked the compound, where bin Laden had been hiding since at least last summer. During a firefight, the U.S. team killed bin Laden, 54, and took custody of his body in what Obama called “the most significant achievement to date in our nation’s effort to defeat al-Qaeda.”

At the White House early Monday afternoon, Obama said: “I think we can all agree this is a good day for America. Our country has kept its commitment to see that justice is done. The world is safer. It is a better place because of the death of Osama bin Laden.”

Speaking at a ceremony to award Medals of Honor posthumously to two Korean War veterans, Obama added: “Today, we are reminded that, as a nation, there’s nothing we can’t do when we put our shoulders to the wheel, when we work together, when we remember the sense of unity that defines us as Americans.”

The discovery that bin Laden had been hiding in a well-populated part of Pakistan, rather than a remote location, raised new questions about the extent to which Pakistan is cooperating with the United States in combating terrorism.

U.S. forces flew to bin Laden’s hideout in helicopters about 1 a.m. Monday (4 p.m. Sunday in Washington) from neighboring Afghanistan. Bin Laden was killed after he and his guards resisted the U.S. attackers, a senior Obama administration official said. U.S. personnel identified him by facial recognition. Bin Laden was shot in the head, the Associated Press reported.

Brennan said the U.S. team was prepared for the “remote” contingency of capturing bin laden alive, as well as what officials viewed as the greater likelihood of a gun battle. “If we had the opportunity to take him alive, we would have done that,” he said.

He said U.S. officials are talking to the Pakistanis to “pursue all leads to find out what sort of support system” and “benefectors” bin Laden had in Pakistan, given that he was living in a house that “had the appearance of a fortress” and that clearly stood out from the surrounding neighborhood.

“It does raise questions” about why Pakistani authorities did not investigate it, he said.

Brennan also said the raiders seized unspecified materials from bin Laden’s compound that will be analyzed for their intelligence value. He declined to elaborate on the materials.

The death of bin Laden is a “defining moment” in the war against terrorism and represents “decapitating the head of the snake that is al-Qaeda,” Brennan said.

He said al-Qaeda now faces a problem because bin Laden’s deputy, Ayman al-Zawahiri, “is not charismatic” and has “a lot of detractors in the organization.” He predicted that “you’re going to see them eating themselves more and more.”

Earlier, a U.S. official said the SEAL team quickly flew bin Laden’s body by helicopter back to Afghanistan, where it was positively identified. Then, the official said, the body was taken out of Afghanistan and “buried at sea,” in part because the U.S. government did not want an accessible gravesite that could become a shrine for bin Laden’s followers. The body of water where the burial at sea took place was later identified as the northern Arabian Sea.

A senior defense official told reporters at the Pentagon that bin Laden’s body was buried at sea from the aircraft carrier USS Carl Vinson after traditional Islamic rites including the washing of the corpse.

According to the official, bin Laden “was killed by U.S. bullets” in a firefight at the compound that lasted nearly 40 minutes.

A senior U.S. intelligence official said bin Laden was first “visually identified” at the compound by U.S. Special Operations Forces as well as one of his wives, who survived the raid and later identified him by name. The Special Operations Forces also compared the corpse to photographs of bin Laden “with 95 percent certainty that the body was Osama bin Laden,” the senior intelligence official said.

On Monday morning, U.S. officials completed tests that showed a “virtually 100 percent match of the body” with DNA collected from other bin Laden family members.

U.S. officials declined to say whether an autopsy was conducted.

The U.S. intelligence official said there was “no indication that the Pakistanis were aware that Osama bin Laden was at the compound” and that intelligence on the compound was not shared outside the U.S. government.

Bin Laden “was more or less hiding in plain sight” and living “high on the hog” with his family on the second and third floors of the house, which sat behind 18-foot walls, with privacy walls on the balconies, the official said.

He said bin Laden and the other three men at the compound “certainly did use women as shields.” Besides the wife who was killed, two other women were wounded, the official said. There were also children at the compound.

The dead woman was later identified as a wife who was deliberately placed in the line of fire, Brennan said. “She was positioned in a way that indicated she was being used as a shield,” he said.

During the raid, one U.S. helicopter broke down. The crew destroyed the helicopter with explosives, so as not to leave the technology behind, and U.S. forces exited on the remaining aircraft.

“All non-combatants were moved safely away from the compound before the detonation” of the helicopter, a U.S. official said.

In Abbottabad, there was conflicting information on who owned the house and on details of the raid. Two Abbottabad residents who live near the compound said the people who lived in the house were Pashtuns from the Swat Valley. One said two brothers lived there, one of whom was a contractor who built the house in 2005.

Another Abbottabad resident said the inhabitants of the house were from South Waziristan, a tribal area along the border with Afghanistan, and that some occupants seemed to be Arabs.

A Pakistani security source said one of bin Laden’s wives and a daughter were taken to the Combined Military Hospital in Abbottabad after the raid, the wife with a bullet wound in the leg. The official also said that the owners of the house were two Afghans named Tariq and Arshad.

A Pakistani intelligence official initially claimed early Monday that the raid was a joint operation carried out “primarily” by the Inter-Services Intelligence agency, contradicting U.S. officials who said it was conducted in strict secrecy by Americans without previously informing Pakistani intelligence, which has long been viewed as riddled with Taliban sympathizers. The Pakistani official later said the raid was “based on intelligence input from us” but that Pakistan did not participate. The discovery that bin Laden was living close to Pakistani military installations was embarrassing “to an extent, yes,” the official said. “Had we known, we would have taken him out.”

U.S. government facilities around the world were placed on heightened alert after the raid, while the State Department issued a worldwide travel alert warning of “enhanced potential for anti-American violence given recent counter-terrorism activity in Pakistan.”

CIA director Leon Panetta told his agency that terrorist groups around the world “almost certainly will attempt to avenge” bin Laden’s death.

“We must — and will — remain vigilant and resolute,” Panetta wrote in a congratulatory memo. “But we have struck a heavy blow against the enemy. The only leader they have ever known, whose hateful vision gave rise to their atrocities, is no more. The supposedly uncatchable one has been caught and killed.”

According to the private SITE Intelligence Group, which monitors radical Islamist Web sites, jihadists threatened retaliation Monday against Americans for the death of bin Laden. One called for attacks on American tourists. Another warned that those who celebrate the killing will face men “who do not fear death and who will reap your souls.” Yet another wrote that Americans should expect to see “hell.”

Secretary of State Hillary Rodham Clinton vowed Monday that the United States “will continue to take the fight to al-Qaeda and its Taliban allies.” Appearing before reporters at the State Department, she said: “Even as we mark this milestone, we should not forget that the battle to stop al-Qaeda and its syndicate of terror will not end with the death of bin Laden.”

She added: “Our message to the Taliban remains the same, but today it may have even greater resonance. You cannot wait us out. You cannot defeat us. But you can make the choice to abandon al-Qaeda and participate in a peaceful political process.”

George J. Tenet, director of the CIA at the time of the Sept. 11 attacks, expressed gratitude Monday on behalf of “those of us who worked against bin Laden and al-Qaeda going back to the mid-1990s, across three administrations.”

“This act of courage and professional discipline, hopefully, will bring healing to families who lost loved ones on the USS Cole, at our embassies in East Africa, the World Trade Center, Pentagon and the fields of Pennsylvania,” Tenet said. “We must also never forget the families of our allies around the world who have also suffered from heinous acts of terrorism inspired by bin Laden.”

But Anthony H. Cordesman, a military and terrorism expert at the Center for Strategic and International Studies, said bin Laden could gain some posthumous stature. “Extremists and terrorists are likely to admire the fact that Osama is reported to have died fighting, and that the U.S. had to destroy one of the helicopters used in the raid,” he said. “They will take the same comfort if reports are correct that two bin Laden couriers, and one of Osama bin Laden’s sons, were also killed in fighting the SEALs.”

The killing of the terrorism mastermind who had eluded U.S. forces for nearly a decade drew a spontaneous, cheering crowd late Sunday outside the White House gates and at New York’s Ground Zero, the site of al-Qaeda’s 2001 attacks on the World Trade Center.

“We will be relentless in defense of our citizens and our friends and allies,” a somber Obama said Sunday night in his nine-minute statement that aired live on television worldwide. “We will be true to the values that make us who we are. And on nights like this one, we can say to families who have lost loved ones to al-Qaeda’s terror: Justice has been done.”

Bin Laden’s killing will provide a clear moment of victory for Obama at a time of deep political turmoil overseas that is upending long-standing U.S. policy in much of the Muslim world, particularly the Middle East.

It also comes nearly 10 years after bin Laden orchestrated the deadliest terrorist attack on U.S. soil, when al-Qaeda terrorists hijacked three passenger jets and crashed them into the World Trade Center and the Pentagon and crashed a fourth jet in rural Shanksville, Pa.

“Today’s achievement is a testament to the greatness of our country and the determination of the American people,” Obama said. “The cause of securing our country is not complete, but tonight we are once again reminded that America can do whatever it is we set our mind to. That is the story of our history.”

Years in the making

The secret operation that culminated with bin Laden’s death was years in the making. For most of the past decade, bin Laden was thought to be hiding in Pakistan, but American intelligence had lost his trail until picking up fresh intelligence of his possible whereabouts last August.

After months of studying intelligence and reviewing operational plans, Obama gave the order on Friday morning for the action that ended in bin Laden’s death. The operation took place in Abbottabad, a city of about 100,000 in Pakistan’s Khyber Pakhtunkhwa province, about a two-hour drive north of Islamabad. Named for a British military officer who founded it as a military cantonment and summer retreat, it is the headquarters of a brigade of the Pakistan army’s 2nd Division.

A Special Operations team conducted the mission based on CIA intelligence, some of which was obtained from detainees in U.S. custody, according to senior U.S. officials who detailed the operation under the condition of anonymity.

“We’ve been staring at the compound for months trying to figure out for sure whether we had enough to go with,” one official said. Operatives have “been working this target for years, years, years. They finally found the guy who led to the guy who led to the guy who led to the guy, and this is it.”

Beginning in September, the CIA began to work with Obama on a set of intelligence assessments, which led him to believe that it was possible that bin Laden might be located at the compound.

By mid-February, Obama determined that there was a sound intelligence basis for pursuing this theory and developing courses of action in case it proved correct. He held five National Security meetings in the second half of March to discuss potential action.

On Friday, shortly before flying to Alabama to visit tornado-ravaged communities, Obama gathered senior officials in the Diplomatic Room. At 8:20 a.m., he made the decision to undertake the operation.

National security adviser Thomas E. Donilon prepared the formal orders and convened senior national security officials that afternoon to plan for the operation. The United States did not share any intelligence with foreign governments, including Pakistan’s, and only a “very small number” of people within the U.S. government knew about it, one official said.

Throughout the afternoon Sunday, Obama met with senior officials in the Situation Room for briefings on the operation. At 3:50 p.m., Obama learned that bin Laden was tentatively identified, and the president remained “actively involved in all facets of the operation, ” a senior administration official said.

The courier

The operation hinged almost entirely on the hunt for a single man: a courier working out of Pakistan who had been trusted by bin Laden for years.

U.S. analysts and operatives spent years figuring out the courier’s identity, senior administration officials said, concluding that he was a former protege of Khalid Sheik Mohammed, the self-declared mastermind of the Sept. 11 attacks who is being held at Guantanamo Bay, Cuba. The courier “had our constant attention,” one official said.

Detainees “identified this man as one of the few al-Qaeda couriers trusted by bin Laden, [and] indicated he might be living with or protecting bin Laden,” the official said. But until four years ago, the United States was unable to track the courier down or uncover his real name. In 2009, U.S. officials narrowed down the region in Pakistan where the courier was working, senior administration officials said.

Then, in August, U.S. officials found the compound that turned out to be bin Laden’s hiding spot. It was described as an extraordinary place, with 12- to 18-foot security walls, multiple interior walls dividing the property and massive privacy walls blocking even a third-story balcony.

“When we saw the compound . . . we were shocked by what we saw,” the official told reporters, describing it as “an extraordinarily unique compound,” built perhaps in 2005 and expressly for bin Laden. “Everything we saw . . . was perfectly consistent with what our experts expected bin Laden’s hideout to look like.”

A senior official said the property, valued at $1 million, had no Internet or phone service. But photos appeared to show a satellite dish at the property, indicating that it had television reception.

Bin Laden’s death offered a sense of closure for families of those lost in the 2001 attacks. Basmattie Bishundat, whose son, Kris Romeo Bishundat, died at the Pentagon on Sept. 11, was glued to her television in the Maryland suburb Waldorf in the early hours of Monday, wishing she could join the revelers at the White House.

“I cannot believe it, finally,” Bishundat murmured as she watched the pictures from the White House on CNN. “All kinds of emotions. Finally, a sense of closure. Finally, they’ve got the person who started all of this mess.”

With the 10th anniversary of the Sept. 11 attacks approaching this year, bin Laden’s assassination could benefit Obama domestically even more than the capture of former Iraqi dictator Saddam Hussein helped propel then-President George W. Bush to reelection in 2004.

Obama called Bush and former president Bill Clinton, as well as senior congressional leaders, before announcing bin Laden’s death to the nation.

Although Bush and former officials were quick to declare bin Laden’s killing a victory that transcended party lines, it represented the culmination of the former president’s promise, never fulfilled during his time in office, to capture the al-Qaeda leader “dead or alive.”

In a statement, Bush congratulated Obama and the military and intelligence personnel who “devoted their lives to this mission.”

“They have our everlasting gratitude,” Bush said. “This momentous achievement marks a victory for America, for people who seek peace around the world, and for all those who lost loved ones on September 11, 2001. The fight against terror goes on, but tonight America has sent an unmistakable message: No matter how long it takes, justice will be done.”

Obama announced bin Laden’s death eight years to the day after Bush declared the end of major combat operations in Iraq, a war spawned in large part by the Sept. 11 attacks, in front of a “Mission Accomplished” banner on the deck of an aircraft carrier.

Condoleezza Rice, Bush’s secretary of state, said in her own statement: “Nothing can bring back bin Laden’s innocent victims, but perhaps this can help salve the wounds of their loved ones.”

Victory for U.S.

Bin Laden, the son of a billionaire Saudi Arabian contractor, was wanted by the United States not only for the Sept. 11 hijackings but also for al-Qaeda’s bombings of U.S. embassies in Tanzania and Kenya in 1998, which killed 224 civilians and wounded more than 5,000 people. The U.S. government had offered a $25 million reward for information leading to his capture or death.

He was one of a handful of Islamist radicals who in 1988 founded al-Qaeda — which means “the base” in Arabic — to coordinate the efforts of various groups fighting the Soviet army in Afghanistan. After the Soviets withdrew from Afghanistan, al-Qaeda eventually shifted its effort to target another superpower: the United States.

A senior administration official said the loss of bin Laden puts al-Qaeda “on a path of decline that will be difficult to reverse.”

“As the only al-Qaeda leader whose authority was universally respected, he also maintained his cohesion, and his likely successor, Ayman al-Zawahiri, is far less charismatic and not as well respected within the organization, according to comments from several captured al-Qaeda leaders,” the official said. “He probably will have difficulty maintaining the loyalty of bin Laden’s largely Gulf Arab followers.”

That bin Laden was killed — rather than captured — was a victory itself for U.S. officials, who had dreaded the prospect of a long and complicated legal battle if he was taken into U.S. custody.

With the military brig at Guantanamo Bay no longer being used to house new detainees, and with the country paralyzed by the politics of where and how to try other alleged perpetrators of the Sept. 11 attacks, the logistics of trying bin Laden could have turned the capture into a spectacle. Now, although he might become a martyr to his supporters, it will be as an invisible hero.

“Every day he was alive was a symbolic victory,” said Dan Byman, director of research at the Saban Center for Middle East Policy at the Brookings Institution and professional staff member on the 9/11 Commission. “This is a man we have hunted with different degrees of intensity for more than 10 years. . . . His successful defiance was damaging to the United States.”

Washington reacts

Obama’s announcement on Sunday seemed to electrify Washington and indeed the country. Hundreds of people streamed toward the White House with flags, some chanting “U.S.A.! U.S.A.!” In New York, many more were celebrating at Ground Zero and in Times Square.

Before Obama announced the killing, top administration officials divided up the most senior members of Congress and began making calls in the evening, according to congressional aides in both parties. Vice President Biden contacted Senate Minority Leader Mitch McConnell (R-Ky.); Defense Secretary Robert M. Gates called Sen. John McCain (Ariz.), the top Republican on the Senate Armed Services Committee; and Secretary of State Clinton called Sen. John F. Kerry (D-Mass.), chairman of the Senate Foreign Relations Committee.

Senior congressional leaders issued statements commending the military for the killing.

“Today, the American people have seen justice,” House Homeland Security Chairman Peter T. King (R-N.Y.), whose Long Island district lost many in the 2001 attacks, said in a statement. “In 2001, President Bush said, ‘We will not tire, we will not falter and we will not fail.’ President Bush deserves great credit for putting action behind those words. President Obama deserves equal credit for his resolve in this long war against al-Qaeda.”

Kerry urged vigilance, saying: “A single death does not end the threat from al-Qaeda and its affiliated groups.”

“The killing of Osama bin Laden closes an important chapter in our war against extremists who kill innocent people around the world,” Kerry added. “We are a nation of peace and laws, and people everywhere should understand that our 10-year manhunt was in search of justice not revenge.  Terrorists everywhere must never doubt that the United States will hunt them down no matter where they are, no matter how long it takes.”

Rep. Gary Ackerman (D-N.Y.) told CNN: “We’ve cut the head off of the worm, but they may grow another head.”

Minutes after the news broke on Sunday night, hundreds of people rushed to the White House to celebrate. Many were George Washington University students who were cramming for finals when someone alerted an entire dormitory building after seeing a bulletin on television.

“I feel like relief,” said freshman Molly Nostrand, 19, who was a fourth-grader in 2001. “After 10 years, it’s a sense of closure in a way.”

Those who arrived early to the impromptu street celebration sang “The Star-Spangled Banner” in roars and chanted “U.S.A.!” Many brought American flags and some put together signs.

“Ding, Dong, Bin Laden is Dead,” one read.

One group of waved a “Bush-Cheney 2000” election poster.

“I think it’s an accomplishment for the U.S. of A.,” Richard Indoe, 73, a farmer from Ohio said, shortly after filming a few seconds of the revelry using a flip cellphone. “Too bad this didn’t happen during George W. Bush’s time.”

Staff writers Philip Rucker, Anne E. Kornblut, Karen DeYoung, Ernesto Londoño, Glenn Kessler, Paul Kane, Felicia Sonmez and Amy Gardner contributed to this report.