Coalition airstrike in Syria mistakenly kills 18 US-backed fighters The position was originally identified as the location of ISIS fighters.

 -- An airstrike on Tuesday by the coalition fighting ISIS south of Tabqah, Syria, killed 18 U.S.-supported fighters, U.S. Central Command announced.

The strike killed members of the Syrian Democratic Forces, a local group of fighters that the U.S. and a coalition of 67 other nations and organizations support in the shared goal of defeating ISIS.

"The strike was requested by the partnered forces, who had identified the target location as an ISIS fighting position," CENTCOM said in a statement.

Instead, the position was occupied by members of the SDF, 18 of whom were killed as a result.

"The coalition's deepest condolences go out to the members of the SDF and their families," the statement continued. "The coalition is in close contact with our SDF partners who have expressed a strong desire to remain focused on the fight against ISIS despite this tragic incident."

The statement further said that the coalition is investigating the strike and planning to "implement appropriate safeguards" to avoid further misdirected action.

Coalition airstrikes are a regular tool in the fight against ISIS in Syria and Iraq. Syria's ongoing civil war — a conflict with origins unrelated to ISIS but during which the group has been able to make inroads in the country — has presented complications in combating the group. Last week's U.S. missile strike on a Syrian air base was the first U.S. engagement in Syria unrelated to the fight against ISIS.

ABC News' Elizabeth McLaughlin contributed to this report.