Pakistan, July 22 -- Militants in Pakistan have started using commercially acquired quadcopter drones to drop bombs on security forces in the country's northwest, police said, a potentially dangerous development in the volatile region.

The use of such drones, which are powered by four rotors allowing for vertical take-off and landing, is worrying the overstretched and under-equipped police force, the frontline against militant attacks, officials said.

Two quadcopters sent by the militants targeted a police station earlier this month, killing a woman and injuring three children in a nearby house in Bannu district, said police officer Muhammad Anwar.

A drone spotted over another police station on Saturday was shot down with assault rifle...