Pakistani security forces partially reopened a key northwest supply route for Western troops in Afghanistan Friday, three days after shutting it to drive militants from the area, officials said. Security forces backed by helicopter gunships, tanks and heavy artillery on Tuesday launched the operation in the rugged Khyber tribal area near Jamrud, the gateway to the famed Khyber Pass linking Pakistan and Afghanistan. The offensive, prompted by a series of attacks on truck depots in and around the city of Peshawar that saw hundreds of NATO vehicles torched, forced the closure of the highway from Peshawar to the Afghan border town of Torkham.