Iraqi police say insurgents have attacked an Iraqi army checkpoint northeast of Baghdad, killing six Iraqi soldiers and wounding 15 others.

Police say Iraqi troops returned fire at the insurgents, killing one of them. The attack took place early Monday near Baquba.

In another incident, Iraqi and U.S. troops raided a Shi'ite militia stronghold in Baghdad before dawn, sparking a gun battle with militants that killed at least three civilians.

The U.S. military says the joint raid took place in the Sadr City district of eastern Baghdad. Officials say the aim of the operation was to catch extremists involved in torture cells and revenge attacks.

Officials say Iraqi and U.S. forces came under fire, and fought the militants for several hours. Local authorities say three civilians were killed in the crossfire, including a woman and a three-year-old girl.

A U.S. soldier and at least 12 other people were wounded. Reports of insurgent casualties are unconfirmed.

In a separate incident late Sunday, the U.S. military says three American soldiers were killed by a roadside bomb southwest of Baghdad.

Also Sunday, a suicide bomber detonated explosives at a funeral in Tikrit, killing at least 10 people and wounding about 20 others.