The ambulance exploded outside a local security building in Baquba [EPA]

At least 12 people have been killed after a suicide bomber detonated an ambulance packed with explosives outside a security headquarters in central Iraq, officials said.

Another 55 people were said to be wounded in the attack on Wednesday.

The attack occurred at around 10am, in the middle of the ethnically-mixed city of Baquba, north of the capital Baghdad.

The blast occurred near the front gate of the Facilities Protective Services compound, which
houses the local headquarters and training grounds for the Iraqi security force tasked with guarding government buildings.

"I was on my way to the market close to the building when I saw the ambulance arrive at the entrance," Sumaya Sabr, who suffered wounds to her head in the blast, said from her hospital bed in Baquba.

"The guards tried to speak to the driver, and when they got close to the ambulance, it blew up. I can't remember anything else - I woke up in the hospital."

Vehicle curfew

Baquba is the capital of Diyala province, which was an al-Qaeda stronghold as recently as 2008. While violence has dropped both in Diyala and nationwide since then, the province remains one of Iraq's least secure.

Local officials imposed a vehicle curfew on Baquba, not allowing any cars in or out, and security forces cordoned off the scene of the blast.

About 90 minutes later in the nearby town of Ghalbiyah, a suicide bomber blew up his explosives-filled car in the middle of a crowd of Shia pilgrims, killing two people and wounding 15 others, Azzawi said.

At least 49 people were killed in former leader Saddam Hussein's hometown of Tikrit on Tuesday when a suicide bomber attacked a line of police recruits.

Hundreds of recruits had gathered outside a police station to be among the first applicants for 2,000 newly created interior ministry jobs.

Authorities said the suicide bomber joined the crowd, then detonated his explosives-packed vest.

Police also found an unexploded grenade at the scene, indicating the bomber was using other weapons to maximise the blast.

Tikrit is located 130km north of Baghdad.