The Iraqi government has imposed an indefinite curfew in Baghdad after one of the worst days of violence since the US invasion in 2003.
Six car bombs killed 160 people in the Shia stronghold of Sadr City in the bloodiest attack to date in Baghdad.
Leaders from all main communities, including Shia Prime Minister Nuri al-Maliki and the Sunni Vice President, made a televised appeal for calm, a step last taken in February when the bombing of a major Shi'ite shrine, blamed on al Qaeda, launched a wave of sectarian bloodshed that has not abated.
Two men scream in anguish as they wait to collect the remains of their brother who was killed in today's attack
"We call for people to act responsibly and to stand together to calm the situation," a joint statement read.
A further 257 people were wounded in the series of blasts in the capital's Sadr City slum, police said.
The blasts came at the same time as gunmen surrounded and fired on the Shia-run Health Ministry in one of the boldest daylight assaults by militants in Baghdad. Mortars later crashed down on a nearby Sunni enclave in an apparent reprisal attack.
After dark, there was sporadic gunfire in several districts.
In Sadr city, parked vehicles packed with explosives caused carnage in streets and a market, a police general told state television. Mortars also landed nearby and residents seized a seventh car they said was driven by a would-be suicide bomber.
"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."
Heavily guarded and policed by the Mehdi Army militia of radical Shia cleric Moqtada al-Sadr, Sadr City was until this year relatively unscathed by al Qaeda and other Sunni insurgent attacks. A string of bombings against civilians there in recent months is seen as a declaration of war on the militia that Sunnis blame for much of this year's death squad violence.
The bloodshed may heighten sectarian anger after a week of tension inside the US-backed national unity government. Washington is pressing Shi'ite and minority Sunni leaders to rein in militants to halt a slide towards all-out civil war.
Noting that today was the seventh anniversary, by the Islamic calendar, of the killing of Sadr's father by Saddam Hussein's agents, Sadr ally Fattah al-Sheikh blamed "terrorist groups and Saddamists" as well as the US occupation and vowed: "Sadr City will be the rock on which all conspiracies will founder."
Another Shia politician, Sami al-Askari, called for the arrest of the main Sunni leader in parliament, Adnan al-Dulaimi, for inciting sectarian violence.
Five people were wounded at the Health Ministry, about 5 km from Sadr City, an Interior Ministry source said, when guerrillas fired mortars, rocket-propelled grenades and machineguns into the compound. The arrival of US helicopters and troops dispersed the assailants, ministry employees said.
Shortly afterwards, a dozen mortar rounds hit Adhamiya, an enclave of Iraq's Sunni minority in mainly Shia east Baghdad. The Interior Ministry said 10 people were wounded in the attack.
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 yesterday violent deaths among civilians had hit a record of more than 3,700 in October.
In the worst attacks in Iraq, 171 people were killed in a series of bombings at Shia religious ceremonies in 2004. Last year, 125 died in a single blast in the Shi'ite city of Hilla.