BAGHDAD -- One of Iraq's most influential Shiite clerics, Muqtada al-Sadr, says he has decided to quit politics, distancing himself from any political movement that uses his name.

Al-Sadr has made such announcements before, but the current declaration comes only two months before national parliamentary elections. Sadrists hold 40 out of 325 seats in the legislature, making them the largest single Shiite bloc, and hold six Cabinet seats.

In the late Saturday statement, al-Sadr said his move was to "preserve the reputation of the al-Sadr (family)... and to put an end to all the wrongdoings that were conducted, or could be conducted, under their title." It did not explain further.

"I announce here that I will not interfere in politics. There is no political entity that represents me anymore nor any position in parliament and government," it said. "Whoever acts against this will be subjected to legal and religious action." He also ordered all al-Sadr political offices to be closed down.

The move did not appear to be expected. Al-Sadr officials could not be reached for contact. The movement announced a news conference, only to cancel it.

Al-Sadr came to prominence in the 2003 U.S.-led invasion that toppled Saddam Hussein, whose regime killed his father and grandfather. He established his Mahdi Army militia that fought the Americans and is blamed by many Iraqis for much of the sectarian violence that raged in Iraq in 2006 and 2007.

Meanwhile, Iraq's main al Qaeda breakaway group claimed on Sunday responsibility for an audacious attack on a military barracks that killed 15 troops last week.

The troops were assigned to protect an oil pipeline that sends Iraqi crude oil to international markets, as well as to guard a nearby highway outside the northern city of Mosul. Eight of the soldiers were beheaded in the Monday attack while the rest were killed by gunfire.

Along with the statement, posted on a website commonly used by jihadists, the Islamic State of Iraq and the Levant put up an image of the beheading of one of the soldiers, as well as captured arms and vehicles. They statement also listed other attacks against security forces in and around Mosul, about 360 kilometres northwest of Baghdad.

The authenticity of the statement couldn't be independently verified, but its style was consistent with previous statements.

Violence continued on Sunday.

Gunmen attacked a police checkpoint outside the northern city of Kirkuk, killing five policemen, said Col. Abbas Hussein. Armed with weapons fitted with silencers, the gunmen first shot two policemen who were manning the checkpoint then moved to a trailer to kill the rest, Hussein added.

In Baghdad's northern neighbourhood of Chikok, a parked car bomb ripped through a commercial area, killing four civilians and wounding 14 others, a police officer and a medical official said on condition of anonymity, as they were not authorized to release information.

Iraq is undergoing a surge in violence, its worst since 2008, which has become the Shiite-led government's most serious challenge. Violence has spiked since last April, when security forces cracked down on a Sunni protest camp north of Baghdad. According to the UN, 8,868 people were killed in Iraq last year -- the country's highest death toll since a peak of sectarian bloodletting in 2007.