The road through the Khyber Pass in the northwest of Pakistan has come under increasing attacks by militants seeking to squeeze Western forces fighting a resurgent Taliban in Afghanistan in recent months.
U.S. and NATO soldiers in landlocked Afghanistan rely on the winding, mountainous route for delivery of up to 75 percent of their fuel, food and other logistical goods, which arrive in Pakistan via the port city of Karachi.
American commanders insist the attacks are not disrupting their mission in Afghanistan, but they also say they are exploring new routes. They also say they have enough supplies to last many weeks in the case the routes are blocked.
The road has been temporarily closed to traffic at least twice this year for security reasons, each time for no longer than several days.
Fazal Mehmood, a civilian administrator in Khyber, said the army launched an offensive against insurgents there Tuesday morning after they ignored a deadline to surrender.
"Because of these operations, supplies have been suspended to Afghanistan and vice versa," he told The Associated Press, giving no details on the offensive or how long the suspension was expected to last.
Gunmen have staged a series of raids on truck depots near the Pakistani city of Peshawar in recent weeks, killing several guards and burning hundreds of vehicles, including dozens of U.S.-bought Humvees destined for the Afghan army.
During the summer, militants attacked and torched dozens of U.S. supply trucks on Afghanistan's main highway.
A smaller number of supplies arrive in Pakistan by a second land crossing at Chaman in the southwest. That road was open Tuesday, a witness said.
NATO says it is investigating other possible supply routes to Afghanistan - such as through central Asian states to its north. The alliance and U.S. officials say the escalating attacks on the Khyber and temporary suspensions are not affecting operations in the country. Guns and ammunition are not shipped through Pakistan.
On a normal day, some 300 trucks carrying military supplies travel up the pass. Media reports have said that truck companies are becoming increasingly unwilling to transport the goods because of the danger.