BAGHDAD —  American troops and Iraqis unearthed 37 bodies Thursday in a mass grave northeast of Baghdad, the U.S. military said.

The site of the grisly discovery was near Muqdadiyah, an area that has seen frequent fighting between American troops and Sunni insurgents led by Al Qaeda in the volatile Diyala province.

The military did not provide further details and Iraqi officials in the area did not have any information about the find in Muqdadiyah, about 60 miles north of Baghdad.

Mass graves have been turning up with increasing frequency as U.S.-led operations have cleared insurgent strongholds with an influx of troops and a Sunni revolt against Al Qaeda in Iraq that have allowed access to former no-go zones.

Including Thursday's find, at least 594 bodies have turned up in mass graves since last May, half of them in Diyala, according to an Associated Press tally.

The mass graves found in former Al Qaeda territory help explain the decision by Sunni tribal leaders to fight back. U.S. and Iraqi commanders say the groundswell helped drive Al Qaeda from the belts around Baghdad and forced extremists to hunt for new havens in northern Iraq.