(CNN) -- Militants in Pakistan's tribal region attacked a truck carrying supplies for NATO troops in Afghanistan -- killing the driver and his assistant, officials said Friday.
Gunmen opened fire and threw petrol bombs, setting the truck and its container on fire, said Muhammad Arshad Khan, a senior government official in Khyber Agency. They then fatally shot the occupants of the truck, Khan said.
The torched truck was part of two-truck convoy headed toward the Torkham border crossing. The second truck was not damaged in the incident.
Pakistan had closed off the crossing after U.S. helicopter strikes across the border killed two Pakistani soldiers. But it was reopened Sunday. It is the main land route for NATO supplies crossing from Pakistan to Afghanistan.
Convoys have repeatedly come under militant fire in recent days. Since October 1, at least six people have been killed in attacks on supply vehicles -- in addition to the latest casualties.
The convoys are generally operated by contracted Pakistani firms, using Pakistani trucks and drivers.
The Pakistani Taliban has claimed responsibility for some of the attack, saying they were in retaliation for drone strikes.
The group said it has set up a special squad to hit U.S. interests in Pakistan, especially NATO supply efforts.
The latest suspected drone strike came Friday when four alleged militants were killed in North Waziristan, two Pakistani intelligence officials said.
Two missiles hit a vehicle in the area of Machi Khel in the district -- one of seven in Pakistan's volatile tribal region bordering Afghanistan.
The intelligence officials asked not to be named because they are not authorized to speak to the media.