By Angela Dewan CNN

(CNN) -- The US-led coalition has killed 18 of its own allies in Syria in what it described as a misdirected airstrike.

The strike was carried out on Tuesday and killed members of the Syrian Democratic Forces (SDF), which Washington and other nations have backed and coordinated with to fight ISIS militants in the country.

"The strike was requested by the partnered forces, who had identified the target location as an ISIS fighting position. The target location was actually a forward Syrian Democratic Forces fighting position," the US Central Command said in a statement Thursday.

"The coalition's deepest condolences go out to the members of the SDF and their families. 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 said that the coalition was assessing the incident.

The airstrike was carried out south of Tabqa, a focus area for the coalition as it closes in on the ISIS heartland of Raqqa.

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