BEIRUT (AP) — A misdirected airstrike by the U.S.-led coalition earlier this week killed 18 allied fighters battling the Islamic State group in northern Syria, the U.S. military said Thursday.

U.S. Central Command said coalition aircraft were given the wrong coordinates by their partner forces, the predominantly-Kurdish Syrian Democratic Forces, for a strike intended to target IS militants south of their Tabqa stronghold, near the extremists’ de facto capital, Raqqa.

The strike hit an SDF position instead, killing 18. Central Command said the strike was launched Tuesday.

Several nations have lent their air power to the U.S.-led coalition to defeat the Islamic State group. It was not clear which air force was behind the strike.

The SDF acknowledged the strike on Thursday, saying a number of its fighters were killed and wounded.

The SDF-linked Hawar News Agency reported the group was holding funerals for 17 of its fighters in the border town of Tal al-Abyad.