BAGHDAD: A suicide bomber with explosives hidden beneath his traditional robe blew himself up on Tuesday in a crowd of Iraqis trying to join the police force, killing at least 25 people in Iraq's second major bombing this week.

The attack occurred in the town of Jalula, a remote, impoverished community in Diyala province about 125 kilometres northeast of Baghdad.

Initial reports from cops said the bomber detonated an explosives laden vehicle near a building where the recruits for a new police emergency response unit had assembled.

Later, however, Diyala Operations Centre and Jalula police said the bomber mingled with crowd and then detonated explosives hidden beneath traditional dishdasha robe. The explosives were packed with nails and ball-bearings to maximise casualties, police said.

He detonated the explosives near a parked car, leading police to conclude the attacker used a car bomb, police said.

US military officials said five policemen were among the dead. A police guard Falah Hassan, 28, said he was standing at the gate of the Jalula police compound, when he heard a thunderous explosion about 90 metres away.

"I saw burned bodies, wounded people and small pools of blood," said Hassan, speaking from a hospital bed in the northern town of Sulaimaniyah, where some of the 40 wounded had been taken.

The local police chief, Col. Ahmed Mahmoud Khalifa, said jobs in police are prized in Jalula, as unemployment runs high.