DAMASCUS, Syria — The U.S.-led coalition fighting ISIS in Syria and Iraq announced Sunday that a strike killed an ISIS leader in Syria who was tied to the death of a U.S. citizen.

Army Col. Sean Ryan, a spokesman for the coalition, said the strikes on Sunday were against “a senior ISIS member, Abu al Umarayn, and several other ISIS members.”

“Al Umarayn had given indications of posing an imminent threat to coalition forces, and he was involved in the killing of American citizen and former U.S. Army Ranger Peter Kassig,” Ryan said. “He has been linked to and directly involved with executing several other prisoners as a senior ISIS member.”

The U.S.-led coaltion has conducted hundreds of air and artillery strikes aimed at driving ISIS from its last remaining pocket of territory in Syria.

The announcement followed a U.S. strike on Saturday that killed a senior Taliban leader in Afghanistan’s Helmand province, a U.S. military spokesman told CNN.

“We can confirm a U.S. airstrike conducted yesterday resulted in the death of Taliban shadow governor Mullah Manan,” Army Col. Dave Butler, a spokesman for U.S. forces in Afghanistan, said. “We’re driving toward a political solution. This killing doesn’t have to continue.”

Manan was the political and military leader of the Taliban in Helmand, one of the insurgency’s most critical strongholds and the origin of much of its drug revenues. A U.S. military official told CNN that a drone strike killed Manan.