The Iraqi government announced a one-day ban on private vehicles in Baghdad and its outskirts aimed at averting violence on Friday, when Muslims attend the most important prayer service of the week.

The ban will take effect when the overnight curfew ends at 6 a.m. Friday and will last until 4 p.m., according to a statement issued by the prime minister's office. Police and army were instructed to seal off the capital and seize any private vehicles that defy the ban.

Hundreds of Iraqis have been killed since the Feb. 22 bombing of a revered Shiite shrine in Samarra unleashed a wave sectarian violence. An extraordinary daytime curfew and vehicle restrictions helped curb the worst of the sectarian killing, but attacks continued this week.

Earlier in the day, a bomb ripped through a vegetable market in a Shiite section of Baghdad, and a leading Sunni politician escaped an attack on his convoy as at least 36 people were killed in unrelenting violence, pushing Iraq toward civil war.

An aide to Prime Minister Ibrahim al-Jaafari , meanwhile, lashed out at Sunni, Kurdish and secular political leaders who have mounted a campaign to deny him another term, saying the Shiite United Iraqi alliance will not change its candidate.

Al-Jaafari met with representatives of the main political parties Thursday night to discuss ways of containing the sectarian attacks, reversing an earlier decision to cancel the meeting after the move against him.

Adnan al-Dulaimi, a leader of the Sunni's largest parliamentary bloc, escaped an assassination attempt Thursday because he already had sped away from the scene in another vehicle in his convoy after the car in which he had been riding got a flat tire. Gunmen opened fire on the disabled car, killing one of al-Dulaimi's bodyguards and wounding five others. The politician said he was not aware of the attack until he reached his office.

The attack occurred a day after it was revealed that al-Dulaimi had joined with key Kurdish and secular politicians in agreeing Wednesday to ask the main Shiite bloc to withdraw al-Jaafari's nomination for prime minister. Shiite officials confirmed receiving a letter Thursday asking them to put forward a new candidate.

The bid has raised a new hurdle in U.S.-backed talks on an inclusive government, which broke down after the mosque attacks.

The State Department said that overall talks on forming a new government were continuing, and deputy spokesman Adam Ereli called the move against al-Jaafari part of "rough-and-tumble" politics.

Separately, a U.S. soldier was killed Wednesday during combat in Iraq's insurgency-ridden Anbar province, the military reported Thursday. At least 2,296 members of the U.S. military have died since the war began in March 2003, according to an Associated Press count.

Many Sunnis blame al-Jaafari for failing to rein in commandos of the Shiite-led Interior Ministry alleged to have committed widespread human rights abuses against them. Kurds are angry at al-Jaafari for purportedly dragging his heels on resolution of their claims around the oil-rich city of Kirkuk.

"We hold him responsible for all the lives that have been lost ... We don't think that al-Jaafari is the right prime minister for the very critical situation that Iraq" is going through, another leader of the Sunnis' largest parliamentary bloc, Tariq al-Hashimi, told AP Television News.

Al-Jaafari adviser Haider al-Ibadi accused the prime minister's critics of trying to delay the formation of a new government, telling The Associated Press: "There are some elements who have personal differences with al-Jaafari."

The decision also drew sharp opposition from the anti-American cleric Muqtada al-Sadr, whose support enabled al-Jaafari to win the nomination over Vice President Adil Abdul-Mahdi by a single vote in a Feb. 12 caucus of Shiites who dominate the new parliament.

An official close to al-Sadr described the attempt to remove al-Jaafari as a "flagrant interference."

"We will not abandon al-Jaafari and this is the right of the people who voted. None of the politicians can impose their will on the people," the official said on condition of anonymity because of the sensitive nature of the political flap.

Al-Sadr's militiamen were believed behind many of the attacks against Sunni mosques last week, and the prospect of a prime minister in debt to the young radical Shiite cleric has alarmed mainstream politicians, including some in the Shiite alliance.

Al-Dulaimi's blood-splashed, bullet-riddled car was carried away on a flatbed truck.

The Sunni leader played down the attack, telling Al-Jazeera TV: "This incident should not be a reason for strife. Iraq is bigger than Adnan and his guards."

A convoy of Defense Minister Saadoun al-Dulaimi's bodyguards was attacked in the same Baghdad neighborhood, police said. Six bodyguards were rushed to Yarmouk Hospital, where one died of his injuries, said Dr. Muhanad Jawad. The minister, a Sunni Arab who is not related to Adnan al-Dulaimi, was not in the convoy at the time.

The explosion during the busy morning shopping period at a vegetable market in Baghdad's southeastern Zafaraniyah neighborhood killed at least eight people and wounded 14, said police Lt. Bilal Ali Majid. The blast damaged nearby shops and left a large crater amid up-ended vegetable baskets and rubble. Police evacuated the market after finding a second bomb.

Another bomb exploded in a minibus traveling through Sadr City, a Shiite ghetto in east Baghdad, killing five people and wounding 10, police said. A fourth device went off as Interior Ministry commandos drove through the mostly Sunni Amariyah neighborhood in western Baghdad, killing one of them and injuring three, police said.

Earlier, gunmen attacked a joint police-army checkpoint about 20 miles north of Samarra, killing six soldiers and four policemen, police said. The attackers set fire to the bodies before fleeing the area, he said.

Four more policemen were killed when gunmen intercepted they vehicle in Mosul, 225 miles northwest of Baghdad, said police Brig. Abdel Hamid al-Jbouri. And police found the bodies of five men apparently shot to death in and around Baghdad on Thursday.

A Sunni cleric was gunned down as he left a mosque after dawn prayers Thursday in Basra, in the southern Shiite heartland.

The slaying came as the head of the government's Sunni Endowment, which takes care of Sunni mosques and religious shrines, announced that 45 Sunni preachers and mosque employees have been killed since the latest round of sectarian violence broke out last month.

It was not clear whether Sheik Ahmed Abdul Ghafour al-Samaraie included the cleric killed Thursday in his count.

He also said 37 Sunni mosques were destroyed and 86 damaged by grenade, rocket or gunfire, while six others remained in the hands of Shiite militiamen. U.S. military officials put the figures much lower.

The former U.N. human rights chief for Iraq said abuses are as bad now as they were under Saddam Hussein. Extrajudicial killings and torture are soaring, and morgue workers are being threatened by both government-backed militiamen and insurgents not to properly investigate deaths, he told AP in Sydney, Australia.

"Under Saddam, if you agreed to forgo your basic right to freedom of expression and thought, you were physically more or less OK," said John Pace, who last month left his post as director of the human rights office at the U.N. Assistance Mission for Iraq. "But now, no. Here, you have a primitive, chaotic situation where anybody can do anything they want to anyone."