The U.S. Military released a statement on Thursday regarding a coalition air strike that incorrectly targeted friendly forces, resulting in the death of 18 allied soldiers engaged in the fight against ISIS near their capital city of Raqqa.

“The Coalition’s deepest condolences go out to the members of the SDF and their families,” CENTCOM said, calling the incident “tragic.”  SDF is an acronym used to describe members of the Syrian Democratic Forces, which includes fighters from a number of groups, including ethnic Assyrians, Turkmen, Armenians and Arabs.  The SDF is primarily made up of Syria’s main Kurdish fighting force, however, the People’s Protection Units, or YPG.

According to CENTCOM, an investigation has been launched into the incident intended to help implement appropriate safeguards to prevent similar incidents in the future.”

The incident took place in the town of Tabqah, approximately thirty miles outside of Raqqa.  Raqqa, the self-declared ISIS capital, is the largest urban center still under the control of the terrorist organization and is the scene of a massing of troops from multiple groups preparing to mount an offensive against fighters inside the city.  The American-led coalition of forces providing air support to the SDF relies on data relayed by ground forces to accurately target and destroy Islamic State fighting positions.

According to a statement released on the official page for Operation Inherent Resolve, the airstrike was requested and relayed by SDF forces on the ground, who identified the spot as an ISIS position.  Unfortunately, it was actually a forward fighting position for allied forces engaged with ISIS fighters.

Journalists inside Syria have conveyed similar accounts, with unconfirmed reports of SDF units withdrawing from the area around Tabqah and blaming the YPG for providing incorrect coordinates for the coalition to engage.

The SDF released a statement confirming that the event took place and indicating that they did not yet know the circumstances that led to the “sad incident.”

US medevac helicopters were seen at the scene of the strike soon after it occurred.  It has not yet been confirmed which group within the Syrian Democratic Forces suffered the casualties, nor has it been confirmed which nation loaning aircraft to the fight against ISIS actually took part in the strike.