Shia movement pulls out of government to protest against US presence.
Also on Sunday, a series of explosions killed at least a further 12 people.
A car bomb exploded near a bus stop a short distance from the municipalities and public works ministry in Bayaa killing at least four people, ministry sources said.
North of Baghdad, two car bombers attacked police positions in Samarra, killing at least eight people in apparently co-ordinated attacks in which armed men also fired mortar bombs, police and army sources said.
Abdullah Jubara, the deputy governor of Salah al-Din province, said Abdul Jalil Naji, Samarra‘s police commander, was killed in one of the attacks, which took place at a police checkpoint.
Meanwhile, US and Iraqi special forces raided a building in Sadr City and called in air strikes.
Several houses in Sadr City were destroyed in
The US army said the raid was against an Iranian-backed Shia armed cell involved in assembling armour-piercing explosives to target US forces.
US forces estimated that between eight and 10 fighters were killed in the raid.
“Coalition forces destroyed a torture room, a large cache of weapons and improvised explosive device-making materials on Sunday morning while targeting terrorists in Sadr City,” the US military said in a statement.
Armed groups fighting the Shia-led government and 150,000 US soldiers in Iraq have switched tactics and stepped up co-ordinated attacks against Iraqi and US security bases.
Fighting broke out during the pre-dawn raid by US and Iraqi forces on Sadr City in which at least six people were wounded. Several houses were bombed out, Iraqi police and hospital officials said.
Aircraft flew over the Shia neighbourhood destroying four homes and reducing one to a pile of rubble, police and witnesses confirmed.
Witnesses said at least one person had been killed and that the number of injured was eight, while police described the attack as an “air strike”.
Several cars were also charred and badly damaged.
One resident, Abu Hammad, said: “We were sleeping and we heard aircraft, both helicopters and planes, flying over us very low and there was lots of shooting so we lay down on the ground.”
The raid appeared to be part of a series targeting members of the Mahdi Army headed by Muqtada al-Sadr, a populist Shia cleric. The fighters have been implicated in sectarian attacks on Sunnis.
‘Triangle of death’
A day earlier, south of the capital, in the so-called “triangle of death”, a bomb exploded in the town of Iskandiriya, wounding 10 people.
Police Lieutenant Karim al-Wael said two of the casualties were in a serious condition.
Late on Saturday, Captain Salam Zankana, of the Kirkuk police, said that three mortar shells crashed down on a southern neighbourhood of the northern oil city killing one woman and wounding four others, among them a child.
US and Iraqi forces are carrying out raids in the town of Yathrib, in the Sunni province of Salah al-Din, after the assassination on Saturday of Jabbar al-Tamimi, a police Colonel.
“Al-Tamimi was visiting a water purification project in the al-Bujaili district in Yathrib when he was attacked by gunmen and riddled with bullets,” a police officer, who requested anonymity, said.
Ten suspects have been arrested, he said.