A moment of silence at the U.S. Embassy in Afghanistan. The reading of names in a grassy western Pennsylvania field. A wreath hung outside the Pentagon. A visit by President Obama to the Arlington National Cemetery graves of 60 U.S. service members killed in Afghanistan and Iraq.

With solemn gestures large and small, Americans across the world marked the 10th anniversary of the Sept. 11, 2001, terrorist attacks on the Pentagon in Virginia and World Trade Center in New York. Ten years after 19 hijackers crashed four jetliners in three East Coast locations, killing more than 3,000 people in the largest terrorist attack on U.S. soil, thousands of mourners returned to those spots under sunny skies reminiscent of the clear blue morning that changed the course of U.S. history.

In response to the attacks, American leaders launched two wars, in Afghanistan and Iraq, with millions of service members dispatching to dangerous locations across the globe. More than 4,000 more Americans have been killed in those conflicts.

At Ground Zero in New York, Obama and former president George W. Bush, along with their wives, walked slowly along the North Memorial Pool, where the north Trade Center tower fell. Obama touched a wall etched with the names of those who perished.

In the crowd, Rosaria Renoe, 40, whose sister, Daniela Notaro, 25, was killed in the attack on the World Trade Center, said she hoped people would never forget the tragedy.

“I want people to be aware of what happened,” Renoe said. “I don’t think there is ever any closure when you lose someone you love so much. You get a bit stronger, but you don’t get over it.”

Opening the New York ceremony, Mayor Michael R. Bloomberg said: “Ten years have passed since a perfect blue sky morning turned into the blackest of nights. Since then, we’ve lived in sunshine and in shadows.”

Obama then read from Psalm 46: “The nations raged, the kingdoms were moved. He uttered his voice. The earth melted. The Lord of Hosts is with us. The God of Jacob is our refuge. Come behold the works of the Lord who has made desolations in the Earth. He makes wars cease to the ends of the Earth.”

Bells chimed at 8:46 a.m., the moment 10 years ago when the first jetliner struck the North Tower, and the crowd observed a moment of silence. Family members began reciting the names of those killed. They stood near the construction site of a new tower, called 1 World Trade Center, a $3.2 billion, 1,776-foot building that has reached the 80th of its planned 104 floors.

The bells chimed again at 9:03 a.m., marking the impact of the second plane flying into the south tower, and Bush read a quotation from Abraham Lincoln. Later, musician Paul Simon played a haunting rendition of “The Sound of Silence.”

Family members paraded images of lost husbands, wives, parents and children on placards, T-shirts, buttons and tattoos. “I love you daddy,” read one card, bearing a photograph.

Chundera Epps, 50, a U.S. postal worker, wore her 29-year-old brother Christopher’s image on a large cape draped over her back. Christopher had worked at an accounting firm on the 93rd floor of the North Tower; it would be three years after the attack before his remains were identified.

“The first Thanksgiving all we did was cry; those kinds of days don’t get any better,” Epps said Sunday. “Life goes on, but the hurt never goes away.”

At the Pentagon on Sunday morning, 1,600 people, including 100 survivors, gathered at the site of the attack on the nation’s military headquarters. Under heavy security, service members laid wreaths on each individual bench at the 9/11 memorial, beneath the backdrop of a huge American flag hanging on the spot the airplane struck.

Vice President Biden paid tribute to the “9/11 generation” of 2.8 million service members who signed up to fight wars in Afghanistan and Iraq, and be deployed in other dangerous regions, in the wake of the terror attacks.

“They relentlessly took the fight to al-Qaeda and its affiliates,” Biden said. “They were prepared to follow [Osama] bin Laden to the hell’s gate if necessary. And they got him.”

Obama left New York and flew to Shanksville, Penn., where United Airlines Flight 93 went down in a grassy field after passengers fought the terrorists in the sky, likely saving hundreds of lives.

The president laid a wreath of white flowers at the center of a marble wall, unveiled at a ceremony the day before, bearing the names of those killed. Several hundred spectators looked on as a children’s choir from Johnstown, a nearby town in Somerset County, sang the national anthem.

After Shanksville, Obama headed to the Pentagon, where he silently hung a wreath at the memorial to the 184 people who lost their lives when the jetliner smashed into the nation's military headquarters.

Obama was scheduled to make remarks at a “Concert of Hope” staged by the Washington National Cathedral at the Kennedy Center on Sunday night. The concert also will feature performances by mezzo soprano Denyce Graves, country star Alan Jackson and R&B legend Patti LaBelle.

Obama, who visited Arlington National Cemetery on Saturday, had said in his weekly radio address: “A decade after 9/11, it’s clear for all the world to see — the terrorists who attacked us that September morning are no match for the character of our people, the resilience of our nation or the endurance of our values. They wanted to terrorize us, but, as Americans, we refuse to live in fear. Yes, we face a determined foe, and make no mistake — they will keep trying to hit us again. But as we are showing again this weekend, we remain vigilant.”

Security was stepped up in Washington and New York, with increased police presence and vehicle checkpoints at New York City’s bridges and tunnels. Federal law enforcement authorities continued to investigate intelligence reports of a potential vehicle-borne bomb attack around the anniversary, possibly involving al-Qaeda operatives.

In Kabul, where U.S. forces have been involved in a war for a decade aimed at eliminating al-Qaeda havens, the U.S. Embassy and Defense Department played host to a gathering including Afghan officials and international military forces. At the symbolic time of 9:11 a.m. local time, guests observed a moment of silence.

“What happened here in Afghanistan and in the United States 10 years ago has joined our two nations forever in a common cause,” U.S. Ambassador Ryan Crocker told the crowd. “Afghan soil must never again be used by elements that would use terror to attack the people of America, Afghanistan and the international community.”

General John R. Allen, commander of NATO’s international security forces, said that coalition troops “have reversed the momentum of the insurgents. On this sacred day of remembrance, I can say we are on the path of success in Afghanistan.”

Yet in a grim reminder of the continuing dangers of the war, NATO said Sunday that 77 NATO soldiers were wounded and two Afghan civilians were killed in a Taliban truck bombing targeting an American base in eastern Afghanistan.

The Taliban released a statement: “It will remain a permanent stigma on the face of Western democracy that America and her allies martyred tens of thousands of Muslims under the pretext of this ambiguous and murky event.”

In neighboring Pakistan, the government reaffirmed “our national resolve to strengthening international cooperation for the elimination of terrorism.”

But in their coverage of the anniversary, the Pakistani media focused on what is widely perceived there as the devastating fallout of the nation’s alliance with the United States after 9/11 — an epidemic of violent religious extremism, a torrent of deadly militant bombings, a teetering economy, massive internal migration and a surge in CIA drone attacks.

“There will be no memorial for those innocents who have died in drone strikes,” the News, an English-language daily, lamented in an editorial. “No books of condolence will be signed for the nameless and unremembered . . . who have died in markets and bazaars or as they walked the streets of their native land.”

In London, British Prime Minister David Cameron, Prince Charles, and U.S. Ambassador Louis Susman laid a wreath at a somber ceremony that included tributes to 67 British victims who died in the terrorist attacks. After the U.S., Britain suffered the most losses during the Sept. 11, 2001 attacks.

Actress Dame Judi Dench, who was wearing a black dress, read a poem called “Remember” while Prince Charles told the assembled guests: “To say that we understand, that we sympathize, that we hold you in our thoughts and prayers is true, but I know it’s hopelessly, utterly inadequate.”

In Paris, a special evening mass was planned at Notre Dame Cathedral while a nine-story replica of the twin towers was erected opposite the Eiffel Tower by a Franco-American organization, “The French Will Never Forget (TFWNF).”

In New York City, Richard Tipaldi, 63, said he couldn’t find words to describe the grief he still feels a decade after the loss of his son, Robert, 25, a trader who was working at Cantor Fitzgerald in the Trade Center during the attacks.

“I’ve been here every year, and it doesn’t get easier,” Tripaldi said. “How do I feel? Empty. The only way I can describe it is you only know it if it happens to you.”

Elaine Barrett, 49, a survivor of the Sept. 11 attack who escaped unharmed from her 92nd floor office at Aon Risk Services in the South Tower, said she has been wracked by guilt for the past 10 years. Her sister, Donna Giordano, who worked on the 103rd floor, didn’t make it out alive.

“I feel tremendous guilt that I got out and she didn’t,” Barrett said.

She said Sunday was the first time that her sister’s son, Michael, 29, who also escaped the World Trade Center, had attended a 9/11 commemoration. Until Sunday, he had felt content to simply revisit the site alone.

Lynch reported from New York City. Staff writers Michael S. Rosenwald at the Pentagon, Shyamantha Asokan in Shanksville, Penn., Karin Brulliard in Islamabad, and Karla Adam in London also contributed to this report.