An airstrike by the American-led coalition fighting the Islamic State killed 18 Syrian fighters allied with the United States, the military said on Thursday.
The strike, on Tuesday in Tabqah, Syria, was the third time in a month that American-led airstrikes may have killed civilians or allies, and it comes even as the Pentagon is investigating two previous airstrikes that killed or wounded scores of civilians in a mosque complex in Syria and in a building in the west of Mosul, Iraq.
Tuesday’s strike was requested by coalition allies who were on the ground near Tabqah, the United States Central Command, which oversees combat operations in the Middle East, said in a statement. The fighters had called in the airstrikes and “identified the target location as an ISIS fighting position,” it said, using another name for the Islamic State.
The Central Command statement said that the target location turned out to be a “fighting position” for the Syrian Democratic Forces, who have been fighting the Islamic State alongside the United States.
It was unclear whether the strike came from an American warplane or one from the other coalition partners.
“The coalition’s deepest condolences go out to the members of the S.D.F. and their families,” Central Command said in the statement, calling the episode “tragic.” Military officials said the cause is being investigated.
As the American-led military campaigns against the Islamic State in Iraq and Syria have intensified in recent months, so, too, have reports of civilian casualties and, now, friendly fire.
Military officials say that is to be expected as Iraqi forces try to retake Mosul in what is seen as the last big urban hurdle to defeating the extremist Sunni militant group in Iraq, and while forces allied with the United States are moving in on the group’s de facto capital of Raqqa, in Syria.
President Trump has indicated that unlike President Barack Obama, who had his White House scrutinize many military operations, he will leave more operational decision-making to the Pentagon and to American commanders in the field.
That move has been welcomed by many in the military, who often expressed frustration at what they saw as a cumbersome decision-making process in Mr. Obama’s White House. But it has raised questions about whether Mr. Trump is exercising sufficient oversight.