The president of the Iraqi Governing Council was killed in a suicide car bombing Monday as his motorcade waited to enter the headquarters of the U.S. occupation authority.

The assassination of Izzedin Salim demonstrated the brutal efficiency of the anti-occupation insurgency six weeks before the United States intends to hand over limited power to an interim Iraqi government. It also infuriated several Iraqi political leaders who have cooperated with the occupation, signaling a difficult time ahead for U.S. officials as they struggle to form a broadly acceptable government.

U.S. military officials also said Monday that a small amount of the nerve agent sarin was detected at the site of a recent detonation of a roadside bomb. The bomb was rigged using an artillery shell that apparently came from an Iraqi army stockpile, but a U.S. military spokesman said whoever rigged the shell probably did not know it contained a chemical agent.

In Washington, Defense Secretary Donald H. Rumsfeld said the presence of sarin had been detected in a field test and could not be confirmed until further tests were carried out.

The discovery of the sarin bomb, which reportedly caused two minor injuries, was announced hours after the attack that killed Salim, a Shiite Muslim who assumed the U.S.-appointed Governing Council's rotating presidency on May 1, and six other Iraqis.

Salim was in a five-car convoy of Nissan Patrols waiting in a line of vehicles to enter the fortified occupation compound known as the Green Zone, on a street well known as a route traveled by Governing Council members. About 9:45 a.m., several witnesses said, a maroon Volkswagen Passat cut out of line and sped toward the Patrol convoy before exploding in flame, smoke and shrapnel.

The blast gouged a hole four feet deep in the pavement and sent several cars somersaulting across the scrub-covered median.

"I tried to hit the car to stop what I saw was going to happen, and suddenly everything exploded," said Ahmed Jawad, Salim's nephew and one of 19 bodyguards with him, who was being treated at Yarmouk Hospital for shrapnel wounds to his face. "I don't know what has happened to my colleagues, whether they are dead or alive."

Military officials said the attack bore the hallmarks of Abu Musab Zarqawi, a Jordanian allegedly linked to al Qaeda. It marked a severe setback in the U.S. effort to stabilize Iraq before the scheduled handover of limited authority. It followed weeks of targeted violence against Iraqi civilians and a politically charged U.S. military operation in the Shiite holy cities of southern Iraq that has inflamed public opinion against the occupation.

Lakhdar Brahimi, the U.N. special envoy who has taken a leading role in forming the interim government, called Salim's killing a "criminal act [that] has taken the life of one of Iraq's most loyal and patriotic citizens."

L. Paul Bremer, the U.S. civilian administrator of Iraq, met at noon with some of the council members to express sorrow over Salim's assassination. In a statement, Bremer said: "The terrorists who are seeking to destroy Iraq have struck a cruel blow with this vile act today. But they will be defeated."

As the country's acting president, Salim was the highest-ranking Iraqi political figure to die in what appears to be an orchestrated effort by the insurgents to target Iraqis working with the occupation authority. He was the second of the original 25 council members to be killed since the panel was formed last July; Akila Hashimi, one of three women on the council, was gunned down on her way to work in September.

Salim, whose given name was Abdul Zahra Othman Muhammad, was a newspaper editor and religious scholar from the southern city of Basra who agitated clandestinely against the government of Saddam Hussein, ousted in April 2003 by the U.S.-led invasion. He was jailed during Hussein's rule for his membership in the once-outlawed Islamic Dawa party, one of the most influential among several Shiite organizations.

Many council members said Monday that complying with the scheduled transfer of some political powers to Iraqis is the best way to deter the insurgency. Ghazi Yawar, a Sunni Muslim council member who was selected to serve the remaining two weeks of Salim's month-long term as president and through June 30, said, "We are determined, more than before, to fulfill the dreams of our lost colleagues.

"History will remember the criminals forever for their shameful actions," he said. "We must always remember our martyr, as well as everyone who was martyred before."

Several council members wept openly in interviews even as they insisted that the planned handover should remain on schedule.

But council members also voiced frustration with the Americans for what they said was a failure to protect Iraqi political leaders or allow them more leeway to protect themselves. The killing increased pressure on U.S. officials to turn over more security responsibilities to Iraqi political parties, something they have been reluctant to do in a country deeply divided along sectarian and political lines.

Dan Senor, chief spokesman for the U.S. occupation authority, said the United States provides Iraqi council members with financial assistance, body armor, vehicles and training to ensure their security -- considerations that, he said, are "second to none."

Salim chose "to rely on cousins and nephews, which was his choice," Senor said. "And unfortunately, our records show that none of his personal security detail members ever participated in any of our training programs -- again, his choice."

In Sunni and Shiite neighborhoods of Baghdad, much of the blame for Salim's assassination was attributed to the U.S. occupation and a Governing Council that many Iraqis consider a powerless American creation. Many people interviewed viewed the killing as part of an erosion of the security situation in much of the country.

From Mosul in the north to Basra, insurgents have been systematically killing Iraqi translators, municipal politicians, tribal sheiks and political leaders working with the occupation authority. The effect has been to isolate the authority from most Iraqis and the intelligence they could provide against the rising insurgency.

"If we had a real government, they would stop the Americans' behavior," said Shafaa Hamed, 41, who owns an electrical supply store in Baghdad's Kadhimiya neighborhood. "The Governing Council members are pawns, and Bremer moves them."

Salim was assassinated 100 yards from an entrance to the Green Zone, the U.S. compound on the grounds of Hussein's former Republican Palace. The blast rumbled through the city, and a column of black smoke washed over the skyline. Apache helicopters buzzed over the area, which was cordoned off with razor wire by U.S. and Iraqi troops.

The bomb charred 17 cars, including most of Salim's convoy. The trunks of nearby eucalyptus trees were blackened, and a small fire continued to burn in the passenger seat of Salim's SUV hours after the attack. Inside the blast crater, a U.S. soldier in rubber gloves picked though the debris for evidence.

Marwan Abta, 42, was getting into his car on his way to work when he saw Salim's convoy speed past. "We're used to seeing these things because of the checkpoint there," said Abta, an engineer. "But I was stunned when I heard the explosion."

Abta heard wailing inside his house moments after the blast, and ran to check on his wife and children. No one was injured, but glass was sprayed across his living room.

"We are in a critical situation," he said. "This is a crime because only civilians are killed. The killer does not have this right."

At Yarmouk Hospital a few miles away, several of the dead and many of the wounded arrived in the frantic ensuing hours. Adel Razzaq, 30, a taxi driver, was being treated for shrapnel in his face. He could not stop crying, although he said it was not from pain.

Razzaq said he and three passengers -- maintenance workers heading to jobs inside the Green Zone -- were in line two cars ahead of the Passat. The driver was honking his horn frantically, he recalled, before darting past his car.

Razzaq watched the Passat pass as he got out of his idling taxi for a cup of tea at a sidewalk stand 50 yards away. The explosion blew him to the ground a few moments later.

"I returned and they were dead, they died in my car," Razzaq said, weeping. "What is our fault? I don't think an Iraqi could do this."

Brig. Gen. Mark Kimmitt, chief spokesman for the U.S. military here, said the explosion bore "the classic hallmarks of what we've seen on Zarqawi attacks," referring to the Jordanian also implicated in the recent beheading of American businessman Nicholas Berg. Kimmitt cited its size, civilian targets and spectacular nature as indicators that Zarqawi could be involved.

At the same time, an organization calling itself the "Arab Resistance Group -- al-Rashid Brigades" asserted responsibility for Salim's killing in a statement posted on the Internet. It called Salim a "mercenary traitor" and vowed to fight on "until the liberation of Iraq and Palestine."

Correspondent Sewell Chan and special correspondents Bassam Sabti, Omar Fekeiki and Huda Lazim contributed to this report.

U.S. soldiers secure the area around a checkpoint near Baghdad's Green Zone after a car bombing that killed Izzedin Salim, who held the rotating presidency of the Iraqi Governing Council. The heavily fortified Green Zone contains the headquarters of the occupation authority.