The main Sunni Arab bloc in Iraq's coalition government says it is suspending participation in the cabinet to protest legal proceedings against one of its six ministers.

Officials with the Sunni Accordance Front announced the move Friday to protest an arrest warrant issued for Culture Minister Asad Kamal al-Hashimi.

Hasimi is accused of masterminding an assassination attempt against another politician two years ago. Sunni politicians say the charges are politically motivated. Hashimi is in hiding.

In other news, the U.S. military has announced that a roadside bomb killed five U.S. soldiers in southern Baghdad Thursday. The military says insurgents opened fire on the soldiers' patrol after setting off the bomb.

The top U.S. commander in Baghdad, Major General Joseph Fil Jr., says Thursday's attack was at a level of sophistication rarely seen during the war.

General Fil also said some Sunni tribal militias who had fought coalition forces are now joining in the battle against al-Qaida in Iraq. He said the militias are tired of al-Qaida's influence. He spoke to reporters at the Pentagon through a video link to Iraq.

Insurgents Friday bombed an oil pipeline south of Baghdad, spilling crude oil and sparking a large fire.

Also, radical cleric Moqtada al-Sadr has canceled next week's march of Shi'ite followers to the Askariya shrine in Samarra.

A cleric close to Sadr, Asaad al-Nasirie, says the government was not able to ensure the security of marchers to the shrine, which was bombed for the second time earlier this month.

Some information for this report was provided by AP and Reuters.