In the deadliest attack, a suicide bomber killed 18 people and wounded 30 when he blew himself amid dozens of police recruits queuing outside police headquarters in Fallujah, in restive Al-Anbar province.

The attack was a clear bid to stop young men from joining Iraqi security forces.

A number of tribal chiefs in the province have urged young men to join the security forces at the behest of the US military and the Iraqi government to take on the al-Qaeda led insurgency.

Iraqi police also found 36 bullet-riddled bodies of men killed in apparent sectarian killings.

An interior ministry official said 14 bodies were found in eastern Baghdad, added to 20 more from various areas of the capital late Tuesday.

Two more bodies were found in the town of Al-Mussayib, 80km south of Baghdad.

Hundreds of such bodies have surfaced across Iraq, mostly in Baghdad, since the bombing of a revered Shia shrine in February.

Iraq's Sunni Arab leaders blame the country's Shia-led interior ministry forces of operating death squads that carry out extra-judicial killings of Sunni Arabs.

On Wednesday, insurgents also killed eight people, including four college students, in Baghdad's notoriously violent Al-Dura neighbourhood.

"Insurgents set up a checkpoint on the highway in Al-Dura and stopped a minibus full of college students. They pulled four students out of the bus and shot them dead," the interior ministry official said.

Two civilians were killed in an explosion near a popular market in Baghdad's Al-Shuala neighborhood that also left 15 people wounded, he said, and two policemen were killed in Baquba, north of Baghdad.

Meanwhile, parliament convened Wednesday even as Iraq remains without a new government more than four months after elections for the first full-term post-Saddam Hussein assembly.

Prime minister-designate Nuri al-Maliki has said he expects to form the cabinet by May 10.

Deputy parliament speaker Sheikh Khalid al-Attiya told reporters after the end of the parliamentary session that MPs had "discussed the setting up of a committee to look into the issue of amending the constitution."

Iraq's once-dominant Sunni Arabs have demanded sweeping changes, including scrapping of federalism, in the charter approved in a national referendum on October 15.

"We want to change the constitution," said Zhafer al-Ani, spokesman for the Sunni-led National Concord Front, a major parliamentary bloc.

"The present constitution smells of sectarianism and we are trying to change it so it can be a national constitution representing all Iraqis."

He said the front would demand that a Sunni head the committee, as "issues really concern the Sunnis more than any other ethnic group."

"The main issue is federalism ... It is a red line for us ... especially in the south. We are against federalism in the south," he said.

The present charter is strongly backed by the majority Shias and the Kurds who see it offering enough autonomy in the northern Kurdistan region and the southern Shia dominated regions.

Sunni Arabs fear the constitution will lead to the break-up of Iraq and also rob the former elite community of the nation's vast oil wealth.

Iraq's oil reserves are concentrated in the north and south.

Any revised charter would have to be approved by parliament and by a fresh nationwide referendum.

Parliament also discussed alleged Iranian military incursions in the northern Kurdistan region, with the speaker Mahmud Mashhadani demanding a report from the defence and foreign affairs ministries on the affair.

The defence ministry on Monday said Iranian forces entered Iraqi territory on Sunday and shelled the positions of a rebel group, the Kurdistan Workers' Party.

In a rare piece of good news in the strife-torn country, two freed German hostages headed home.

Rene Braeunlich, 32, and Thomas Nitzschke, 28, were freed Tuesday after being held for more than three months by a group called Ansar al-Tawheed wal Sunna (Followers of Unity and Prophetic Tradition).

The two men were working for a German company when they were kidnapped on January 24 as they drove to the Baiji oil refinery, 200km north of Baghdad.

Several of Wednesday's German newspapers reported that a ransom had been paid to secure their release.