Kabulצילום: אייסטוק

Following warnings of an “imminent terrorist attack” expected in the Kabul region, a huge blast was heard in the Afghan capital early Sunday afternoon. Footage shows black smoke rising from a site in the city, around three miles from the airport, and early assessments estimated that the explosion was caused by a rocket attack.

A Pentagon source later told CNN that the strike was by US forces operating a drone, and that it took out an “imminent ISIS-K threat,” referring to the Afghan branch of Islamic State.

“US military forces conducted a self-defence unmanned over-the-horizon airstrike today on a vehicle in Kabul, eliminating an imminent ISIS-K threat to Hamad Karzai International airport,” the source said.

“We are confident that we successfully hit the target,” he continued, noting that “multiple” Islamic State suicide bombers had been heading for the airport in a vehicle. He added that “significant secondary explosions” suggest that the vehicle contained a large amount of explosives.

A child was reportedly killed in the strike, although this has not been conclusively determined. “We are assessing the possibilities of civilian casualties, though we have no indications at this time. We remain vigilant for potential future threats.”

This is the second airstrike the United States has conducted against ISIS-K, which claimed responsibility for last Thursday’s suicide bombing that killed 13 US service members and almost 200 Afghans.

US forces remain on high alert.