Gunmen wearing uniforms, reporter among the dead.

Archive -- a suicide bomb in Tikrit; Dec 3, 2010

Gunmen wearing military uniforms and suicide vests were locked in a shoot-out with security forces Tuesday after storming a Tikrit building in an attack that left at least 52 dead and over 65 wounded, Iraq officials said.

The gunmen swarmed into the building in the city of Tikrit, about 160 kilometers (100 miles) north of Baghdad, immediately after a suicide bomber detonated his payload and cleared the way, a police official said.

A car bomb exploded shortly afterwards as police reinforcements were arriving, he said.

"We received 20 dead bodies and 65 wounded," said a source at the Tikrit General Hospital, the biggest in the city.

"A police colonel, Imad Nofan, and his deputy were killed in the car bombing," the police official said. The same explosion also killed journalist Sabah al-Bazi, who had reported for several local and international news organisations, the police official and other sources said.

It was unclear whether hostages were being held or how many.  Police said employees were still inside the building while witnesses said that at least some had managed to flee the building from another exit.

"Police cannot approach because the gunmen are shooting from inside. The attackers are all wearing suicide belts," a security official said, adding that at least one had detonated his payload inside. He said all were dressed in military uniforms.

The stand-off was still ongoing, four hours after the storming of the building.

The first suicide bombing occurred at 12:40 pm (09:40 GMT), and the car bomb exploded about 20 minutes later, the police official said.

A curfew had been imposed in Tikrit which is the hometown of Saddam Hussein, the Iraqi dictator ousted in the 2003 US-led invasion and later tried and hanged.

Archive -- a suicide bomb in Tikrit; Jan 18, 2011

The province remains the scene of bloody attacks. In mid-January, a suicide bomber blew himself up and killed 50 people in a crowd waiting outside a police recruitment centre in Tikrit.

That blast, which also wounded up to 150, was the first major strike in Iraq since the formation of a new government on December 21.

There was no immediate claim of Tuesday's attack, but officials said it bore the hallmark of Iraq's Al-Qaeda affiliate.

Iraq's security forces are now solely responsible for the country's security, with the United States having declared a formal end to combat operations in the country at the end of August.

Violence across Iraq has declined substantially since its peak in 2006 and 2007, but attacks remain common.