An Iraqi girl walks Wednesday past the scene of an explosion in Baghdad, where a parked car killed 11 people and wounded 13 near a private hospital. ((Hadi Mizban/Associated Press))

At least183 people were killed and dozens were wounded Wednesday in four bomb attacks in Baghdad, the deadliest wave of violence since the start of a joint U.S.-Iraqi security campaign in the capital two months ago.

In the deadliest of the attacks, a parked car bomb detonated in a crowd of workers at the Sadriyah market in a mostly Shia area of central Baghdad, killing at least 127 people and injuring 148, said Raad Muhsin, an official at Al-Kindi Hospital where the victims were taken.

A police official confirmed the toll, speaking to the Associated Press on condition of anonymity because he was not authorized to release the information.

The bomb went off at about 4 p.m. local time, the time construction workers rebuilding shops in the market typically finish work each day. Many shops were destroyed in a previous bombing in February that killed 137 people.

One of the wounded, 28-year-old Salih Mustafa, said he was waiting for a minibus to head home when the blast went off.

"I rushed with others to give a hand and help the victims," he said. "I saw three bodies in a wooden cart, and civilian cars were helping to transfer the victims. It was really a horrible scene."

Late Wednesday, Prime Minister Nouri al-Maliki ordered the arrest of the Iraqi army colonel who was in charge of security in the area aroundthe market.

About an hour earlier, a suicide car bomber crashed into an Iraqi police checkpoint at an entrance to Sadr City, the capital's biggest Shia Muslim neighbourhood and a stronghold for the militia led by radicalShia cleric Muqtada al-Sadr.

The explosion killed at least41 people, including five Iraqi security officers, and wounded 76, police said.

Black smoke billowed from a jumble of at least eight incinerated vehicles that were in a jam of cars stopped at the checkpoint.

Bystanders scrambled over twisted metal to drag victims from the smouldering wreckage as Iraqi guards staggered around stunned.

In the two other bombing incidents:

  • A parked car exploded near a private hospital in the central neighbourhood of Karradah, killing 11 people and wounding 13, police said. The blast damaged the Abdul-Majid hospital and other nearby buildings.
  • A bomb on a minibus in the northwestern Risafi areakilled four people and wounded six others, police said.

Also in Baghdad Wednesday, four policemen were killed in the afternoon when gunmen ambushed their patrol south of the city centre, police said. Six pedestrians were wounded in the gunfire.

In other violence, two brothers were killed and a policeman was hurt in a gun battle in downtown Baqouba, 55 kilometres northeast of Baghdad, police said. The dead were believed to be civilians who were caught in the crossfire as police fought unidentified gunmen.

With files from the Associated Press