Baghdad was under curfew on Friday and the government appealed for calm after car bombs in a Shi'ite stronghold killed 160 in the bloodiest single attack of the war, pushing Iraq closer to the abyss of anarchy.
A further 257 people were wounded in the blasts, which left bloodied remains and blackened bodies scattered amid blazing vehicles. Mortars hit a Sunni enclave soon after, apparently in retaliation for the car bombs, which came as gunmen assaulted the Shi'ite-held Health Ministry in a bold daylight raid.
"It's an extravagant attack specifically designed to trigger retaliation," said Toby Dodge, an Iraq expert at Queen Mary, University of London, likening it to the bombing of a Shi'ite shrine in Samarra in Febuary that sparked a surge in bloodshed.
Iraqi and US leaders accuse al Qaeda and diehard followers of deposed president Saddam Hussein of seeking to provoke a Shi'ite backlash in order to profit from ensuing chaos.
The attacks come after a week of tension inside the U.S.- backed national unity government. Under pressure over Iraq after Republicans were defeated at midterm elections this month, President George W. Bush has pressed Shi'ite and minority Sunni leaders to rein in militants to avoid all-out civil war.
Prime Minister Nuri al-Maliki, who meets Bush next week for a summit in Jordan, warned of "the dark hand of conspiracy that is shedding the blood of the innocent" and urged restraint, vowing to hunt down those responsible. Top Shi'ite, Sunni and Kurdish politicians made a joint appeal for calm.
Authorities slapped an indefinite curfew on Baghdad and closed the airport. Ports and the airport in the southern Shi'ite oil city of Basra would also close, an official said, in protest at the attacks.
Pools of blood
Heavily guarded and policed by the Mehdi Army militia of radical Shi'ite cleric Moqtada al-Sadr, Sadr City escaped relatively unscathed until this year from al Qaeda and other Sunni insurgent attacks. Bombings against civilians there in recent months have been seen as a declaration of war on the militia, which Sunnis blame for a wave of death squad violence.
"As the bombs went off, everyone started running and shouting," news photographer Kareem al-Rubaie said. "I saw a car from a wedding party, covered in ribbons and flowers. It was burning. There were pools of blood ... and children dead."
In a dramatic daylight raid that kicked off Thursday's spasm of violence, five people were wounded when guerillas fired mortars, rocket-propelled grenades and machineguns into the Health Ministry compound, about 5 km (3 miles) from Sadr City.
The Health Ministry is run by followers of Sadr, whose Mehdi Army is accused by many Sunnis of being behind some of the worst death squad violence in the capital, in which thousands of people have been kidnapped and tortured and their bodies dumped.
The United Nations said on Wednesday violent deaths among civilians had hit a record of over 3,700 in October. It said attacks had surged since the Samarra bombing in Febuary and some 420,000 fled their homes to other parts of Iraq since then.
"What you have is anarchy, a war of all against all with no hand strong enough to win," said Dodge, adding that the response to the bombs would test Sadr's ability to control the Mehdi Army. "It's clearly an attempt to get a Samarra-like backlash."
Thursday's attack was the worst single attack of the war and the highest death toll since 171 people were killed in bombings in Kerbala and Baghdad at Shi'ite ceremonies in 2004.
Maliki has called for a swifter transfer of responsibility for security to Iraqi forces. Bush has said he will not leave the 140,000 U.S. troops in the "crossfire" of a civil war in Iraq, but has also vowed not leave without establishing stability and security in Iraq.