The Iraqi government has imposed an indefinite curfew in Baghdad and closed two major airports, after coordinated car bombings and mortar explosions killed 160 people in the Sadr City neighborhood of the capital.
The death toll from Thursday's attack in the densely populated Shi'ite area was reported to be the largest in a single incident since the beginning of the Iraq war in 2003.
Officials say at least five car bombs exploded and several mortar rounds were fired into Sadr City Thursday.
After the attack on the Shi'ite stronghold, more than a dozen mortar rounds were fired into Sunni Arab neighborhoods of Baghdad in apparent retaliation. At least one of the mortars hit an important Sunni mosque.
Iraqi religious and political leaders appeared on television to appeal for calm and an end to the spiraling sectarian violence. A recent U.N. report said more than 37-hundred Iraqi civilians were killed last month.
Earlier in Sadr City, the U.S. military said Iraqi forces and coalition advisers conducted a raid to capture the leader of a kidnapping and murder cell. The military says the cell leader is believed to have knowledge about a U.S. soldier kidnapped in Iraq last month.
Also Thursday, gunmen staged a bold daylight attack on the Shi'ite-run Health Ministry building in Baghdad, sparking fierce clashes with security forces.
Officials say the gunmen surrounded the building and fired mortar rounds, leaving ministry workers trapped inside. The siege ended after several hours. There were no immediate reports of casualties.
The U.S. military says three Marines died Wednesday of wounds sustained in combat action in western Al Anbar province.