Minutes later, a second suicide truck bomber detonated his explosives outside the home of Thamer Ibrahim Atallah, a leader of the Salaheddin Awakening Council, a coalition of tribes established to fight al-Qaeda in the Tikrit area.

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Atallah escaped the attack but five people, including one of his bodyguards, were killed.

The identities of the other casualties were not immediately known. US forces had been deployed in the area after the blasts, al-Bijwari said.

The attacks come a day after a suicide bomber killed 14 people at a police post near Samarra, around 100 km south of Baiji, also in Salaheddin province.

Car and roadside bombs on Monday killed at least 21 people across Iraq. Al-Qaeda had threatened to increase in attacks during the month of Ramadan.

Fighting al-Qaeda

Last Thursday, a roadside bomb near Samarra killed Sheikh Maawia Naji Jebara, the leader of the Salaheddin Awakening Council.

An umbrella organisation of Iraqi armed groups, including al-Qaeda in Iraq, claimed responsibility for the killing in a statement posted on the internet.

"Your brothers ... have succeeded in tracking and assassinating the leader of infidelity and apostasy who is known as Maawia Jebara," the so-called Islamic State of Iraq said.

Sheikh Sabah Mutashar al-Shimmary,the deputy leader of the council, was wounded in the attack on Jebara's convoy. He recently said that his group was making headway against al-Qaeda fighters.

"Our forces are working in co-ordination with the ministers of defence and interior and have conducted more than 100 combat duties against al-Qaeda," Shimmary said.

"We arrested some Arab terrorists including one Saudi ... our troops consist of 3,000 fighters distributed across seven headquarters in the province."

The US military has said that tribal police units have sprung up in a number of provinces to target al-Qaeda fighters, spreading a model first used in al-Anbar province, but they have also become targets for suicide bombers.

Salaheddin province has a predominantly Sunni population. In February 2006, an attack on a Shia shrine in Samarra unleashed sectarian killings across the country.