(Updates death, casualty figures)

BAGHDAD, May 11 (Reuters) - Suicide truck bombers struck police checkpoints on two bridges in a Shi'ite area south of Baghdad on Friday, killing 22 people and wounding 60, police said.

A police source said eight policemen were among the dead, but it was not clear how many casualties were caused by each blast. Twelve policemen were also wounded in the blast, the latest apparent insurgent attack on bridges in Iraq.

Police said the first bomber damaged the old Diyala Bridge and a nearby police station. Minutes later, a few kilometres (miles) away, another attacker detonated his truck bomb on the new Diyala Bridge. There were no immediate reports of damage on that bridge.

The two bridges over the Diyala River, a tributary of the Tigris, are commonly used by Shi'ite pilgrims on their way to the holy Shi'ite cities of Najaf and Kerbala to the south.

Suspected al Qaeda Sunni Arab militants have carried out a series of attacks on bridges in Baghdad in recent weeks. Iraqi and U.S. forces have stepped up security on bridges.

Last month, a truck bomb destroyed the Sarafiya Bridge in Baghdad, sending several cars crashing into the Tigris. Days later a suicide car bomber blew himself up on a ramp leading to another bridge in Baghdad.

Politicians from both sides of the Shi'ite-Sunni sectarian divide have accused insurgents of trying to split the capital of seven million people along sectarian lines.

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