Gunmen wearing explosive belts stormed an anti-terrorism police building in the Iraqi city of Ramadi on Sunday and at least six people died in the attack, police and provincial officials said.

The attack in mainly Sunni Anbar province followed several weeks of bombings targeting Shi'ites after the eruption of a political crisis that has threatened to break up the coalition government and raised fears of renewed sectarian violence.

Three policemen, two of the attackers and a civilian died in the assault on the Ramadi police building, and 14 others, including seven police and seven civilians, were wounded, said Mohammed Fathi, the spokesman for Anbar province.

Police had said earlier the gunmen were holding hostages inside the building and their fate was not immediately clear.

One of the gunmen blew himself up and the other was shot by police, Fathi said.

The Iraqi security forces managed to regain control over the anti-terrorism building and a building beside it. Some of the terrorists were killed, others managed to escape, he said. The situation is under control now.

One gunmen was still shooting from the roof of a local government building, he said.

Ramadi, the Anbar provincial capital, witnessed some of the worst violence during the height of the war that followed the 2003 U.S.-led invasion. It was the heart of a Sunni Islamist insurgency tied to al Qaeda.

Anbar tribal leaders and thousands of Sunni insurgents eventually turned against al Qaeda and formed the Sahwa militia, which joined U.S. forces and helped turn the tide of the war.

Iraqi security officials have expressed concern that al Qaeda may regroup in Anbar following the U.S. withdrawal.

Ramadi's government buildings have been frequent targets of militant attacks.

Violence in Iraq has ebbed since the height of sectarian slaughter in 2006-2007 but Sunni insurgents and rival Shi'ite militias still carry out attacks almost daily. Insurgents often target local government buildings and security forces.

The attack in Ramadi came a day after a suicide bomber killed more than 50 people and wounded more than 100 in an attack on Shi'ite pilgrims passing through a police checkpoint in the southern city of Basra.

Tensions are running high in Iraq four weeks after the last U.S. troops pulled out following moves by the Shi'ite-led government against two Sunni political leaders and a series of bombings that have killed scores of Shi'ites.

(Reporting by Fadhel al-Badrani; writing by Jim Loney and Patrick Markey; Editing by Andrew Roche)