They said explosives may have been attached to the underside of the car belonging to Sheikh Ali al-Nida, head of the al-Bu Nasir tribe.

 

Sheikh Ali's driver was also killed in the blast and at least one of his guards was seriously wounded.

 

The car exploded as it was travelling back to Awja, the executed leader's birthplace, after a trip to Tikrit.

 

Maj Ahmed Subhi, head of a counter-terrorism unit in Salahuddin province, said the sheikh "was the victim of assassination".

"When he left his house there was a bomb in his car that killed him and a driver," Maj Subhi added.

 

 

Members of the al-Bu Nasir, a 20,000-strong Sunni Arab tribe, held some of the most important security and political positions in Iraq under Saddam Hussein.

 

Some security forces - such as the feared Intelligence Service and the Special Republican Guard - were exclusively manned by clansmen from the al-Bu Nasir.

 

Last year, Sheikh Ali founded a so-called Awakening Council in Awja, part of a movement in which Sunni Arab tribes teamed up with US forces to fight al-Qaeda-inspired militants in the area.

 

At the end of 2006, as head of the tribe he received Saddam Hussein's body for burial in Awja following the former leader's execution in Baghdad.

 

Members of the al-Bu Nasir have been targeted before during the five years of violent instability that followed the 2003 US-led invasion of Iraq.

 

Correspondents say it is unclear if the tribe's ties to the late leader were the motive or long-standing tribal rivalries.

 

Mahmoud al-Nida, the sheikh's brother, was killed by unknown gunmen in 2006.

 

Members of Awakening Councils, which are in part credited for the recent reduction in violence in Iraq, have also been frequently the targets of assassination.