At least 26 members of the Pakistani armed forces died Friday when a military transport helicopter crashed in the Northwest Frontier province, officials said.

The pilot sent out a distress call as he flew back to Peshawar from an area near the border with Afghanistan, the BBC reported. The MI-17 helicopter crashed in a Taliban stronghold with militants firing at it, and soldiers sent to the crash site exchanged gunfire with them, officials told the British broadcaster.

Investigators were trying to determine why the helicopter crashed. Officials said the preliminary finding indicated a mechanical problem.

Earlier in the day, The New York Times said, residents of another Taliban-controlled area reported what they called an attack on a remote village by an American drone that killed at least 13 people. An intelligence official confirmed the attack, the Times said.

The Pakistani military is preparing for an offensive in South Waziristan, where Baitullah Mehsud, the leader of the Pakistani Taliban, is based, the Times said.