While local residents in North Waziristan said two missiles fired from a drone aircraft flying out of Afghanistan hit the religious school, Pakistan's Defense spokesman Maj. Gen. Waheed Arshad told reporters the explosion took place when bombs being made by the militants in the school exploded.

Pakistan's The News newspaper reported Wednesday some 50 students and teachers were also in the building and all had been killed or injured.

Another Islamist school and two adjacent houses were badly damaged in the explosion, the Press Trust of India reported.

The region turned into a safe haven for hundreds of al-Qaida and Taliban fighters after U.S.-led forces ousted the Taliban regime from Afghanistan in late 2001.