The victims are believed to include up to six Sunni Arab tribal leaders who had allied themselves to the US military.

They were targeted by a man wearing an explosives belt who blew himself up in the lobby of the Mansour Hotel in Baghdad, which houses the offices of several Western news organisations.

A total of nine people were killed in the blast. Some media reports say the victims included six US-allied tribal leaders, while others say just one was killed.

Elsewhere, up to 18 people were killed when another bomber rammed an explosives-laden truck into the walls outside a police building in the northern oil city of Baiji.

Officials say the dead include police officers and a number of prisoners who were being held at the facility.

Another eight people died when a suicide car bomber detonated his explosives outside the governor's office in the city of Hillah, south of Baghdad, while two Iraqi soldiers were killed in a suicide attack at a checkpoint in the Siniyah area.