A suicide bomber driving an ambulance killed up to 15 people and wounded more than 50 in an attack on Wednesday on an Iraqi police training centre in volatile Diyala province, officials said.

Suspected Sunni insurgents and Shi'ite militia have stepped up attacks in recent months on Iraqi policemen and soldiers, seeking to undermine faith in the security forces before a full U.S. military withdrawal by the end of this year.

Samira al-Shibli, a spokeswoman for the provincial governor said 15 people were killed and 52 wounded in the blast in the city of Baquba, 65 km (40 miles) northeast of Baghdad.

Police sources in Baquba put the death toll at 14, and 64 wounded. Ali Hussein, general manager of Diyala health department, said only five were killed, and 74 wounded.

One police source said there were two attackers. One of them shot dead three security guards at the gates of the training centre, opening the way for a second assailant to drive the ambulance in.

The blast caused part of the three-storey building, where offices for different departments of Iraqi police and security are located, to collapse, said Lieutenant Colonel Hisham al-Tamimi, head of the counter-terrorism department in Diyala.

I can see hands and legs of dead policemen sticking out from under the rubble, said a policeman at the blast site.

Wednesday's attack was the second by a suicide bomber in two days on Iraqi security forces. At least 49 people were killed in former dictator Saddam Hussein's hometown of Tikrit on Tuesday when a suicide bomber attacked a line of police recruits.

That was the bloodiest attack in Iraq since Prime Minister Nuri al-Maliki won support in December for his reappointment, ending a nine-month stalemate that followed a March election.

Overall violence has fallen sharply since 2006-07 peak of the sectarian slaughter between once dominant Sunnis and majority Shi'ites triggered after the 2003 U.S.-led invasion.

But Sunni Islamist groups like al Qaeda still battle Iraqi security forces, particularly in ethnically mixed Diyala, Baghdad and the turbulent northern province of Nineveh, and target the less visible U.S. forces whenever they can.

POLITICS?

Analysts said recent attacks are probably not related to the formation of the new Shi'ite-led government, which includes the Sunni-backed Iraqiya bloc.

Iraqiya won the most parliamentary seats in last year's election and many feared its possible exclusion from power could have led to a surge in violence.

Such explosions are common, due to the security breaches and the inability of the security apparatus to protect the people, said Iraqi political analyst Abdul-Jabbar Ahmed, a professor at Baghdad University.

It is not the first time that such security breaches happen, and it has nothing to do with the Iraqi government leaning towards a specific component.

In a separate incident on Wednesday, a suicide car bomber killed two Shi'ite pilgrims and wounded 16 on a road between Baquba and Baghdad, police sources said.

Attacks against Shi'ites are expected to rise ahead of the religious event of Arbain, which culminates next week. Arbain marks a 40-day mourning period for Imam Hussein, a grandson of the Prophet Mohammad who was killed at the battle of Kerbala in the 7th century and who is a central figure of Shi'ite Islam.

Al-Qaeda Iraq Iraq Iraq