Updated

Police in the past 24 hours have found the bodies of at least 87 people killed by execution-style shootings — a gruesome wave of apparent sectarian reprisal slayings, officials said Tuesday.

The dead included at least 29 bodies stacked in a mass grave in an eastern Shiite neighborhood of Baghdad.

The bloodshed — the second wave of mass killings in Iraq since bombers destroyed an important Shiite shrine last month — followed weekend attacks in a teeming Shiite slum in which 58 people died and more than 200 were wounded.

North of the capital, a roadside bomb exploded Tuesday among Shiite pilgrims headed on foot to the holy city Karbala, killing one person and injuring seven near Baqouba, police said.

With sectarian tension mounting, Iraq's Interior Ministry announced a ban on driving in Baghdad to coincide with the first meeting of Iraq's new parliament Thursday. The ban takes effect at 8 p.m. Wednesday and lasts until 4 p.m. Thursday.

Squabbling over the composition of a new government has delayed the inaugural session since the results of Dec. 15 elections were confirmed more than a month ago.

Leaders of Iraq's main ethnic and religious blocs, meanwhile, began a series of marathon meetings Tuesday to try to break the deadlock. U.S. Ambassador Zalmay Khalilzad, who has been shuttling between the main factions, joined the session hosted by Shiite leader Adbul-Aziz al-Hakim.

The stakes are high for Washington, which hopes a strong and inclusive central government can stabilize Iraq so U.S. forces can start drawing down in the summer.

Interior Minister Bayan Jabr told the AP that authorities had foiled an Al Qaeda plot that would have put hundreds of its men at critical guard posts around Baghdad's heavily fortified Green Zone, home to the U.S. and other foreign embassies as well as the Iraqi government.

A senior Defense Ministry official said the 421 Al Qaeda fighters were actually recruited to storm the U.S. and British embassies and take hostages. Several ranking Defense Ministry officials have been jailed in the plot, the official said on condition of anonymity because of the sensitivity of the information.

Most of the corpses were found in Baghdad, while three were found in the northern city of Mosul, police said.

Acting on an anonymous tip, police found a 6-by-8-yard hole in an empty field. It contained at least 29 dead men — most of them in their underwear — in Kamaliyah, a mostly Shiite east Baghdad suburb, said Interior Ministry Lt. Col. Falah al-Mohammedawi. He estimated they had been dead for three days.

Residents offered scarves to help cover the bodies, which were laid out on the ground. Police guarded the site as members of a Shiite militia dug for more corpses.

An abandoned minibus containing 15 bodies was found Tuesday on the main road between two mostly Sunni neighborhoods in west Baghdad, not far from where another minibus containing 18 bodies was discovered last week, said Interior Ministry official Maj. Falah al-Mohammedawi.

At least 40 more bodies were discovered in various parts of Baghdad, including both Sunni and Shiite neighborhoods, he said.

They included four men shot in the head execution-style and hanged from electricity pylons in Sadr City, where two car bombs and four mortar rounds shattered shops and market stalls at nightfall Sunday as residents shopped for food.

Scores of frightened Shiite families have fled predominantly Sunni parts of Baghdad in recent weeks, some of them at gunpoint. More than 100 families arrived between Monday and Tuesday alone in Wasit province, in the southern Shiite heartland, said Haitham Ajaimi Manie, an official with the provisional migration directorate. More than 300 Baghdad families are now sheltering in the province, he said.

The violence since the Feb. 22 bombing of the famed golden dome atop the Shiite Askariya shrine in Samarra has complicated negotiations for Iraq's first permanent, post-invasion government. A caretaker government has been in charge since the December elections, and U.S. and Iraqi officials fear the vacuum in authority is fueling the bloodshed.

Under pressure from Khalilzad, leaders of the main ethnic and religious groups agreed Sunday to meet daily until they can unblock the political negotiations.

Among the most contentious issues is Shiite Prime Minister Ibrahim al-Jaafari's candidacy for a second term. Kurdish, Sunni and some secular leaders argue he is too divisive and accuse him of doing too little to contain reprisal attacks on Sunni mosques and clerics after the Shiite shrine was destroyed.

The Shiite United Iraqi Alliance is itself divided over al-Jaafari. He won the nomination by just one vote last month in large part because of the support of radical Shiite cleric Muqtada al-Sadr. Al-Hakim favored Adil Abdul-Mahdi, one of two current vice presidents.

Also present at Tuesday's meeting were President Jalal Talabani and Massoud Barzani, leaders of the main Kurdish parties; Dhafir al-Ani, an official with the main Sunni bloc; and former Prime Minister Ayad Allawi, a secular Shiite.

President Bush said insurgents were trying to ignite a civil war by escalating the violence.

"I wish I could tell you that the violence is waning and that the road ahead will be smooth," Bush said in the first of a series of speeches to mark the third anniversary of the start of the U.S.-led war in Iraq. "It will not. There will be more tough fighting and more days of struggle, and we will see more images of chaos and carnage in the days and months to come."

Bomb blasts and shootings in Baghdad and north of the capital, many of them targeting Iraqi police patrols, killed at least 15 more people Monday and wounded more than 40. They included a U.S. soldier who died in a roadside bombing, the military said. A U.S. Marine was reported killed Sunday in insurgent-plagued Anbar province.

The American deaths brought the number of U.S. military members killed to at least 2,308 since the beginning of the Iraq war in March 2003, according to an Associated Press count.

Britain, the United States' largest military partner in Iraq, announced a 10 percent — about 800-troop — reduction by May.

In Paris, a high-ranking U.S. official expressed concern about security in Iraq's oil sector.

Stuart W. Bowen Jr., U.S. special inspector general for Iraq reconstruction, compared the rebuilding program to a three-legged stool built on governance, security and infrastructure: "Each of those legs is a little wobbly right now," he said.

Iraq currently produces 1.7 million to 1.8 million barrels of oil per day — far short of the capacity of 2.8 million and down from a post-invasion peak of 2.4 million last summer, he said.

"The drop, since then, is connected primarily to attacks," he said, adding that U.S. expectations on oil production were too high. "There was an assumption that has proven not to be accurate — that is, that the Iraqis would be able to fund recovery through their oil income."