BAGHDAD, Iraq, March 12 — Six car bombs exploded at dusk today in four crowded markets in a Shiite area of eastern Baghdad, killing at least 46 people and injuring more than 200 others, an Interior Ministry official said, spurring Shiite militiamen to take to the streets.
The explosions, the deadliest single assault in Baghdad in weeks, threatened to unleash a wave of sectarian violence similar to the one that followed the bombing of a revered Shiite shrine last month.
The powerful blasts set vehicles aflame in the Sadr City neighborhood and scattered body parts across city blocks. In the gathering darkness, with ambulances wailing through the streets, black-clad militiamen from the Mahdi Army, which is loyal to the militant Shiite cleric Moktada al-Sadr, raced among the debris and set up checkpoints. Firemen aimed their hoses at charred metal hulks, the arcs of water shooting past dazed people stumbling from the wreckage of market stalls.
"I heard a loud boom; I was inside a bathhouse at the time," said Jafar Thamer Nahee, 25, a metal worker. "I saw tens of people being taken away by ambulances. The police and Mahdi Army surrounded the area. There were Mahdi Army checkpoints all around, and they were carrying weapons."
The scene evoked the aftermath of the Askariya Shrine bombing in the northern city of Samarra on Feb. 22, when the Mahdi Army streamed out of Sadr City and led mobs in attacking Sunni mosques across eastern Baghdad, leaving hundreds dead and pushing Iraq to the edge of a full-scale civil war.
The Iraqi Islamic Party, a conservative Sunni Arab group, quickly released a statement condemning the latest bombings, apparently sensing the potential for deadly anti-Sunni reprisals and, quite possibly, another slide toward civil war.
"Every time the political groups try to start negotiations to reach common opinions among them, we are surprised by a bloody incident aimed at destroying the political process and inflicting more damage among our people," the party said.
The Sadr City bombings took place at about 6 p.m. local time, just after the leaders of all of Iraq's main political blocs met for the first time to discuss forming a government. The leaders had been mired in rancorous sniping over nominations for the office of prime minister, and had not met since Feb. 25, when they had met to address sectarian tensions. At the urging of the American ambassador, the leaders convened in the fortified Green Zone this afternoon, and promptly decided to move up the date of the first session of Parliament to March 16 from March 19.
The ambassador, Zalmay Khalilzad, appeared with the Iraqi politicians in an outdoor news conference afterward and gave an unusually frank assessment of the state of the country.
"I think the situation is such that there's a degree of vacuum in authority," he said. "The need on an urgent basis to form a government of national unity is there."
Early this afternoon, the trial of Saddam Hussein resumed, entering a new phase as the court heard testimony from defendants for the first time. Three of Mr. Hussein's co-defendants, all lower-level former Baath Party officials, denied any role in the torture and killing of 148 men and boys from the Shiite village of Dujail in the 1980's.
At the high-level political meeting, which took place in the headquarters of the Kurdistan Democratic Party, leaders representing the main Shiite bloc, the Kurds, the Sunni Arabs and a secular bloc agreed to tackle later the major issues confronting them: the conflict over the post of prime minister and the definition of a national unity government.
As the politicians met inside a compound, Kurdish militiamen in camouflage fatigues and Shiite militiamen in navy-blue suits hung around on the front lawn beneath palm trees, along with a group of foreign and Iraqi journalists called together at the last minute by the American embassy, in an apparent attempt to exert more pressure on the politicians.
The political parties have reached an impasse in talks because of a conflict over the nominee for prime minister. The Shiite bloc, which has tentative control of the Parliament by holding 130 of 275 seats, has nominated Ibrahim al-Jaafari, the current prime minister and a much-maligned figure, to be its candidate. Under the new constitution, the largest bloc in Parliament can nominate a prime minister.
In early February, the Shiite bloc's 130 legislators held a secret ballot to choose the nominee, and Mr. Jaafari won by one vote, after getting the support of Mr. Sadr, the radical cleric.
But a loose alliance of the Kurds, Sunni Arabs and secular politicians has demanded that the Shiites replace Mr. Jaafari with someone more acceptable. Mr. Jaafari has been widely criticized for failing to quell the rampant violence and improve reconstruction, and he has drawn the anger of the Kurds for making a recent visit to Turkey, a country that often threatens to invade Iraqi Kurdistan in order to suppress any secessionist aspirations among the Kurds.
Mr. Jaafari's office released a statement on this morning suggesting that he intended to fight to keep the nomination. "I think they dealt with it in a democratic way," Mr. Jaafari said. "This is a democratic tradition and we should all respect it and abide by it."
American officials fear a prolonged battle over the new government may embolden the Sunni-led insurgency and inflame sectarian tensions. At least 15 Iraqis were killed and 19 injured in violence between Saturday night and Sunday afternoon, before the Sadr City attacks.
This morning, a roadside bomb exploded by an American convoy in southern Baghdad, killing at least six Iraqi civilians and injuring 13 others, an Interior Ministry official said. Insurgents shot dead an interpreter for the Defense Ministry and an employee of the Culture Ministry in separate incidents. Gunmen killed three other people, and a mortar round killed two civilians and injured six others. Two Iraqi intelligence officers were gunned down Saturday night.
Iraqi policemen found eight bodies, all bound and blindfolded, in Rustamiya neighborhood, and two others in two separate locations.
The six car bombs that exploded in Sadr City ripped through four marketplaces, all crowded with evening shoppers. The police discovered a seventh car bomb that had failed to detonate, the Interior Ministry official said. As the fires burned, Mahdi Army fighters stopped ambulances arriving at the sites to check for explosives.
Militiamen showed up shortly after the bombings in Beirut Square, in a neighborhood bordering Sadr City, and ordered merchants to close up. Though the area was thronged with shoppers, all the stores shut down within minutes and the place emptied out completely.
"Everyone knows Sadr City is the main Shia area in Baghdad and the main support for the Shia alliance," said Ali Saleh Abbas, a follower of Mr. Sadr and the leader of the Ansar Organization, a local charity. "They are trying to put more pressure on the alliance in this bombing. They want the Mahdi Army to revolt."
The American military and Iraqi Army set up checkpoints right outside Sadr City after nightfall, military officials said, presumably to try to prevent sectarian reprisals.
Earlier in the day, at a secured courthouse inside the Green Zone, the defendants in Mr. Hussein's trial appeared one by one to testify before Judge Raouf Abdel Rahman. The defendants have often spoken out in the trial — especially Mr. Hussein and his half-brother Barzan Ibrahim al-Tikriti — but today they were formally given a chance to present their version of the events in the Dujail case.
The session was the first since March 1, when Mr. Hussein acknowledged that he ordered the trial of the 148 men and boys who were executed after an assassination attempt on him in Dujail in 1982. He stopped short of saying he had signed the death warrant that prosecutors displayed as evidence. He defended his action, saying that the men were suspected of plotting to kill him and that he had acted within his rights as Iraq's president.
Today, two of Mr. Hussein's co-defendants described seeing people rounded up and killed after the assassination attempt, but all three denied any responsibility and even portrayed themselves as good Samaritans.
The first defendant, Mizhar Abullah Ruwayyid, said he had been working as a telephone operator at the Dujail telephone exchange at the time, and he insisted that his accusers had grudges against him because he had cut off their phone service for nonpayment of their bills.
The next defendant, Ali Dayih Ali, described seeing Baath Party officials arresting people in the village and war planes bombing the nearby orchards. "Many families were arrested," he said. "Some of them returned, some did not. Most of the youth did not come back."
Mr. Ali said he had been a graduate student at the time of the incident, spending most of his time in the library. He admitted to having arrested one teenage boy in the case. But he did so only under protest, he said, and because his father, the local sheriff, was sick.
Both Mr. Ali and Mr. Ruwayyid disavowed earlier incriminatory statements they had signed for court investigators, saying they had poor eyesight and could not read the documents properly.
The third defendant, Abdullah al-Roweed, said he had seen pickup trucks carrying as many as 10 dead bodies after airstrikes on the orchards. He described himself as a farmer who had been on vacation at the time and "did not even hurt a fly."