WASHINGTON – A U.S. defense official says an American airstrike killed more than 100 al-Qaida militants at a training camp in a remote area in northwestern Syria.

The strike was carried out Thursday by an Air Force B-52 bomber and an undisclosed number of U.S. drone aircraft, the official said. The official was not authorized to publicly announce the attack and so spoke on condition of anonymity.

The militants killed in the airstrikes were described by the official as “core” al-Qaida members, among a number who had moved to Syria early last year to establish a foothold. The official distinguished these militants from members of the group formerly known as the Nusra Front, which is an al-Qaida affiliate in Syria.