BAGHDAD (AP) – An attack against the mayor of Sadr City has created tension in the ranks of Shiite militiamen with some blaming a faction unhappy about cooperation with Americans, a local commander said Friday.

Gunmen opened fire on the convoy carrying Mayor Rahim al-Darraji Thursday in eastern Baghdad, seriously wounding him and killing two of his bodyguards, police and a local official said.

Mr. al-Darraji was the principal negotiator in talks with AmericanU.S. officials that led to an agreement to pull Shiite fighters off the streets in Sadr City, a stronghold of the feared Mahdi Army, and a local commander said suspicion fell on a group of disaffected militiamen who are angry about the deal.

“This is a faction that enjoys some weight,” the Mahdi Army commander said, speaking on condition of anonymity because of the sensitivity of the subject.

He said the attack has created tension within the ranks of the militia and renewed debate about allowing the Americans to operate in Sadr City without resistance during a security sweep aimed at ending the sectarian violence that has raged since a Feb. 22, 2006, bombing of a Shiite shrine in Samarra.

Mr. al-Darraji had also lobbied the Americans to bring reconstruction projects to Sadr City that would create jobs in the impoverished neighborhood. American military commanders have said that could help disarm the largely unemployed men in the Mahdi Army.

One of the dead bodyguards was identified as police Lieutenant Colonel Mohammad Mutashar Al-Freji, a friend of Mr. al-Darraji who was politically linked to radical cleric Muqtada al-Sadr.

The success in reining in Mr. al-Sadr’s Mahdi Army militia, which fought fiercely against American forces in 2004, is widely credited with the drop in execution-style killings, random shootings and rocket attacks during the month-old operation, and the attack against Mr. al-Darraji cast a shadow on that strategy.

Supporters of Mr. al-Sadr also planned a demonstration Friday after traditional weekly prayer services to protest the establishment of a joint American-Iraqi base in Sadr City, a sprawling district in eastern Baghdad.

Four American soldiers, meanwhile, were killed in a roadside bombing Thursday in mainly Shiite eastern Baghdad and the military said it found a sophisticated weapon at the site that was of the type Washington believes is being supplied by Iran to Shiite militias.

Two more American troops were reported killed Friday – an American soldier who died in an explosion Thursday in the volatile Sunni province of Salahuddin, northwest of Baghdad, and a Marine who died in a non-combat incident Thursday in Anbar province, west of the capital. A Marine also died Wednesday in a non-combat incident in Anbar.

At least 74 Americans have been killed in fighting since the American-Iraqi security sweep to stop the sectarian violence in Baghdad began on Feb. 14 – most in Baghdad or volatile areas north of the capital and to the west in the Sunni insurgent stronghold of Anbar province. At least 3,208 members of the American military have died since the Iraq war began four years ago next week, according to an Associated Press count.

American Major General Joseph F. Fil Jr., who is on his second tour of Iraq, acknowledged Thursday that the security crackdown was putting American troops at greater risk in the capital simply because they were in the streets in greater numbers.

General Fil also said America would have American soldiers in as many as 100 garrisons scattered throughout Baghdad by the time the last of the additional 20,000-plus troops allocated by President Bush arrive at the end of May. There are now 77 such posts, he said.

The bases will be a combination of Joint Security Stations – command and control centers operated jointly with Iraqis – and small combat outposts.

In northern Iraq, traffic stopped and people stood still in the streets despite rain for a period of silence in Sulaimaniyah and other Kurdish cities to commemorate the anniversary of a 1988 chemical weapons attack on the Kurdish town of Halabja that killed an estimated 5,600 people and left many still suffering the aftereffects of nerve and mustard gas.

Hundreds of victims’ relatives and local officials gathered in the city hall in Halabja, 150 miles northeast of Baghdad, and lit 19 candles to symbolize the 19 years since the massacre took place.

Saddam Hussein had ordered the attack as part of a scorched-earth campaign to crush a Kurdish rebellion in the north, seen as aiding the Iranian enemy, although the ousted leader was executed on other crimes against humanity before he could face trial for Halabja.

“Each year on this day, I remember the vicious attack carried out by Saddam against the peaceful city,” Tuba Abid, 53, who lost 22 relative in the attack, said as she laid roses on a victims’ monument in Halabja. “The execution of Saddam has reduced my pains and I feel more secure after the death of this dictator.”

Prime Minister Nouri al-Maliki had planned to attend the ceremony, but his plane was unable to land at the airport and was forced to return to Baghdad because of the bad weather, Kurdish officials said.

In other violence Friday, according to officials:

_ Gunmen killed a member of the governmental facilities protection service in Suwayrah, 25 miles south of Baghdad.

_ A police patrol in the northern city of Kirkuk struck a roadside bomb, then was ambushed by gunmen. Two policemen were killed and three civilians wounded.

_ A mortar attack against a Sunni mosque in the southeastern Baghdad neighborhood of Zafaraniyah killed one civilian and wounded two others.

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Associated Press writers Yahya Barzanji in Halabja and Sameer N. Yacoub in Baghdad contributed to this report.