Iraqi authorities have said they had arrested a policeman and six others accused of being al Qaeda members who staged car bombings in Baghdad the day before a visit by US President Barack Obama.

Seven car bombs across the capital on April 6 killed at least 37 people and marked the start of a rise in attacks that have cast a shadow over recent security gains and raised fears Iraq could plunge back into sectarian warfare.

Interior Ministry spokesman Major General Abdul-Karim Khalaf said the group was responsible for a total of 27 attacks, including car bombs and car jackings in which they killed the drivers and used their vehicles for bombs. Three were captured in Baghdad and the rest in western Anbar province.

The men were planning to blow up what would have been the eighth car bomb of the day on April 6 when police found them in Baghdad's southern Doura district, he said.

Subsequent investigations found that a policeman had helped the attackers to get through numerous checkpoints manned by soldiers and police all over Baghdad, he said.

'What is novel about this case is the involvement of a member of the Interior Ministry,' Khalaf said.

The policeman was a Shi'ite Muslim, and not a Sunni Arab like the vast majority of al Qaeda sympathisers and operators, Khalaf said. He said the man was lured into the group by money.

In what the Interior Ministry said was a videotaped confession, one of the detained men said he was a leader of al Qaeda in Haditha in 2005, a town in western Anbar province, that at the time was an al Qaeda stronghold.

Rash of bombings

The announcement of the arrests coincided with growing apprehension in Iraq as U.S. combat forces prepare to pull out of cities in June, ahead of a full withdrawal by the end of 2011, and in the run-up to a national election late this year.

Later the same day, security officials presented a photograph of a man detained last week who they believe is Abu Omar al-Baghdadi, leader of the so-called Islamic State of Iraq, an al Qaeda-affiliated insurgent group.

If the man is Baghdadi, whose capture and death have been reported before, it could be a blow to a group seen as one of the chief insurgent operators in Iraq.

While overall violence has fallen to levels not seen since the 2003 U.S.-led invasion, insurgents like al Qaeda continue to carry out suicide and car bomb attacks regularly.

Two days of suicide bombings last week killed more than 150 people, many of them Shi'ite pilgrims from neighbouring Iran, raising the spectre of renewed fighting between once dominant Sunnis and majority Shi'ites.

US forces in Iraq have not yet said whether they believe the detained man is Baghdadi.

While Iraqi officials earlier said they would conduct a DNA test to confirm Baghdadi's identity, security spokesman Major General Qassim Moussawi said on Tuesday that such a test would be impossible because there was no previous information on him.

Baghdadi 'is a high-value target whose arrest will give Iraqi forces the opportunity to follow the strands of this group, pursuing its members and arresting them,' government spokesman Ali al-Dabbagh told al-Arabiya television.

He said Baghdadi would be referred to an Iraqi court.

'The government understands that al Qaeda is still a threat to the security situation, and our alert level remains high. We imagine they will try to retaliate but we have no choice but to face them with everything we've got,' Dabbagh said. – Reuters