WASHINGTON — Suicide — not combat — is the leading killer of U.S. troops deployed to the Middle East to fight Islamic State militants, according to newly released Pentagon statistics.

U.S. casualties have been relatively low since the U.S.-led war effort began with a bombing campaign in August 2014, reflecting the limited combat exposure for troops. Of the 31 troops who have died as of Dec. 27 in Operation Inherent Resolve, 11 have taken their own lives. Eight died in combat, seven in accidents and four succumbed to illness or injury. The cause of one death is under investigation.

The reasons suicide ranks as the No. 1 cause of troop deaths are complex and poorly understood, according to experts on military suicide. They likely include mental illnesses that enlistees brought with them to boot camp, post-traumatic stress, multiple combat deployments and heightened anxiety in a military at war for 16 years.

Read the full story at USA Today.

In this November 2015 file photo, an airstrike by a U.S.-led coalition warplane explodes on an ISIL position in Syria. (Photo: John Moore, Getty Images)