On Tuesday militants blew up a bridge in northwest Pakistan, cutting the main route for supplies bound for Western forces in Afghanistan.

This attack has been the latest and perhaps most serious, attempt to block supplies to the U.S.-led mission against the Taliban. Guards are usually posted on heights above bridges but it was not clear why they had been unable to stop the attack.

The 30-meter (100-foot) iron bridge, 23 km (15 miles) west of the city of Peshawar, was blown up after midnight and officials said all traffic along the route was suspended.

The length of the slender metal bridge slanted to one side and was blocked by an overturned truck that spilled dozens of dusty bags into the pavement. Traffic from the bare hills continued on foot, with Afghans and Pakistanis, including women in burqas, hurrying their baggage over the dry riverbed.

A NATO spokesman in Afghanistan said supplies along the route had been halted for the time being, but stressed the alliance was in no danger of running out of food, equipment or fuel, the Associated Press reported.

The latest attack on the famous Khyber Pass highlights the urgent need NATO and the U.S. have for alternative supply routes to landlocked Afghanistan through nations to its north, especially as the U.S. plans to double its troop numbers in the country this year.

Up to 75 percent of the fuel and supplies destined for U.S. and NATO troops in Afghanistan travel through Pakistan after being unloaded at the port of Karachi and most are driven along the Khyber Pass.

Whether supply convoys are able to reach Afghanistan through smaller routes in the region is not immediately clear.

According to spokeperson, Fazal Mahmood, repair work had begun on the bridge.

Pakistan Afghanistan U.S.