JALALABAD, Afghanistan — At least 13 people were killed by an airstrike in the eastern Afghan province of Nangarhar on Wednesday, with officials describing the victims as members of the Islamic State, while some residents claimed the dead were civilians.

A United States military spokesman, Brig. Gen. Charles H. Cleveland, said that a “counterterrorism airstrike” had taken place in the area on Wednesday but that he could not discuss details. He added that the military “takes all allegations of civilian casualties very seriously” and that a review of the strike was underway.

Afghan officials said the victims of the strike, in the Achin district, were members of the Islamic State, also known as ISIS or ISIL. The district has long been a hotbed of Islamic State activity, one of the few in Afghanistan.

The provincial police in Nangarhar issued a statement saying that 18 Islamic State members were killed in the strike, in the Shadal Bazaar area of the Achin district, including an Islamic State judge and a local commander.