Two U.S. service members were killed and five others were injured Sunday while conducting combat operations in northern Iraq, officials with Combined Joint Task Force-Operation Inherent Resolve said in a statement.

Initial reports indicate the incident was not due to enemy contact, officials said.

“An army artillery section was conducting a counter-fire mission against an ISIS mortar site when a mishap occurred, injuring seven soldiers,” Pentagon spokesman Army Col. Rob Manning said Monday. “There is no indication that ISIS had anything to do with this. The injured soldiers were [evacuated by air] and two of the soldiers subsequently died.”

“The other five soldiers did not suffer life threatening injuries,” Manning said.

Manning did not know whether the artillery equipment misfired or if the mishap was the result of human error, and that the incident is under investigation.

“The entire counter-ISIS Coalition sends our deepest condolences to these heroes’ families, friends and teammates,” said Lt. Gen. Stephen Townsend, commander of Combined Joint Task Force-Operation Inherent Resolve, in a statement. “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.”

Pentagon bureau chief Tara Copp contributed to this report.