Two U.S. service members were killed and five others were injured during combat operations in northern Iraq on Sunday, the military announced in a statement.

The joint task force against the Islamic State in Iraq and Syria, Operation Inherent Resolve, said an investigation has been opened into the incident. According to the statement, initial reports suggest the casualties did not come as a result of "enemy contact."

"The entire counter-ISIS Coalition sends our deepest condolences to these heroes' families, friends and teammates," Lt. Gen. Stephen J. Townsend, commander of the task force, said in the statement Sunday.

"There are no words to describe the respect I have for you and sorrow I have for your loss," Townsend continued. "I hope there is some small solace in knowing their loss has meaning for our country and all the nations of the Coalition as the fallen service members were fighting to defeat a truly evil enemy and to protect our homelands."

As NPR's Lauren Frayer reports, nine Americans involved in the operation have been killed this year, and nearly 50 service members have been wounded since the campaign was launched roughly three years ago.

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