Higher Education Minister Abed Dhiab al-Ujaili, a Sunni member of Iraq's Shia-led national unity government, would not return to work until all of the 70 to 80 hostages still believed held had been freed, a ministry spokesman said.

“The minister has stopped working,” said spokesman Basil al-Khateeb.

While acknowledging he had no exact figure for the number of hostages seized in Tuesday's audacious raid by militiamen in military-style uniforms, Khateeb took issue with assurances from government spokesman Ali al-Dabbagh that nearly all had now been freed.

“Thirty-two were released today (Wednesday), while the others were freed yesterday (Tuesday),” making 70 in all, Khateeb said.

But he insisted that between 70 and 80 more continued to be held.

The government spokesman had earlier played down the scale of the kidnapping insisting that only 39 people had been abducted, of whom all but two had been released.

The withdrawal of the Sunni minister marked a new blow for the embattled national unity government of Prime Minister Nuri al-Maliki, which has faced mounting criticism for not doing more to prevent Shiite militia infiltration of the security forces.Mr Maliki vowed that the authorities would hunt down those responsible for the kidnapping, regardless of rank, saying that their crimes were worse than those of the militants of Al Qaeda.

“I do not need only the captives to be released, but I also want those who did that act,” the premier said at Baghdad university during a visit to calm shocked professors and students.

“The country is full of such gangs and militias but this will not drive us back from chasing them.”The authorities already detained five police commanders in connection with the abductions on yesterday lending credence to Sunni Arab allegations that Shiite militias are operating death squads with the connivance of elements of the security services.

The interior ministry and the security forces under its command have long been a particular target of Sunni suspicions.

“This cowardly act confirms what we have always warned and we blame the government and the interior ministry for this crime,” said Iraq’s leading Sunni ulema’s organisation, the Muslim Scholars’ Association.

But the US-led forces’ outgoing commander for the Baghdad region, Major General James Thurman, voiced confidence that the interior ministry was taking strong action to track down the kidnappers.

“I think the minister of interior -- I talked to him five times yesterday about that -- he was very upset and we worked that operation all night and ran several tips that we actioned on and I've seen his determination,” Thurman said.

His successor Major General Joseph Fil said ministry forces had been active throughout the night. “I can tell you they had three operations last night that I know of -- there may have been many more -- where they very proactively and aggressively were chasing them down,” he said.

In other violence, a powerful car bomb killed 12 people at a petrol station near the interior ministry in central Baghdad, while 18 bullet-riddled bodies were found south of the capital, officials said.

In Baquba, north of Baghdad, two civilians were shot dead.

—AFP