A suicide bomber has blown himself up in a crowd of Iraqi police recruits, killing 28 people and wounding 45, police said.

It was the biggest attack for weeks in Iraq, which has been enjoying some of its lowest levels of violence in four years.

It came amid Iraqi efforts to conclude a security deal with the United States that would allow American forces to leave Iraq by the end of 2011.

A police source said the bomber, wearing an explosive vest, struck a large crowd lining up to apply to join the police in the town of Jalawla, in Iraq's volatile Diyala province, north of Baghdad.

No one has claimed responsibility for the attack but recruitment centres have been frequent targets by militants in the past.

Meanwhile, police in the same region have released a video claiming to show a teenage girl attempting to carry out a suicide attack.

The footage appears to show the girl shouting from the side of the road wearing an explosives belt and chained to a metal structure.

The 15-year-old is shown being questioned and denying that she was attempting to cause an explosion.

Officers claim the girl was wearing a belt packed with 33 pounds of explosives.

US commanders in Iraq believe many women are recruited as suicide bombers as they are able to hide explosives under their robes.

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