BEIRUT (AP) — Syrian opposition activists say Friday prayers were cancelled in parts of northern Syria that are held by rebels after an airstrike on a mosque killed at least 40 people.

The Britain-based Syrian Observatory for Human Rights and Bahaa al-Halaby, an opposition activist based in northern Syria, say such decisions are not uncommon where mosques have been targeted in the past.

The decision came hours after an airstrike hit a mosque in the Jeeneh area, near the rebel-held province of Idlib. The Observatory said the airstrike killed 46 while Local Coordination Committees said 40 were killed.

The powerful ultraconservative Ahrar al-Sham group said the airstrike was carried out by the U.S.-led coalition, adding that it was a "war crime."