The two rival Palestinian factions have failed to heal their political disputes since Hamas fighters expelled Fatah from Gaza in a short war in 2007
In a statement the military said the incident was under investigation. The service members were part of a US-led coalition fighting the Islamic State in Iraq.
"The entire counter-ISIS Coalition sends our deepest condolences to these heroes' families, friends and teammates," said Lieutenant General Stephen Townsend, commander of the Combined Joint Task Force - Operation Inherent Resolve.
"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."