Islamist militants in Pakistan blew up a bridge through the mountainous Khyber Pass early on Tuesday, severing a key supply route for US and NATO troops in Afghanistan. Periodic attacks on the route have pushed the international forces to seek alternative ones outside Pakistan.

All traffic on the bridge has come to a halt, The Press Trust of India reports, including dozens of supply trucks bound for US and NATO forces.

The bridge connects Peshawar, the largest city in the Northwest Frontier Province, with the Khyber Pass, the primary route into Afghanistan.

Militants have harassed NATO supply lines in northwest Pakistan for several months, conducting ambushes on convoys and attacking truck depots in Peshawar itself, according to the news service. It says Tuesday's bridge attack may be a result of increased security at supply depots.

The Associated Press reports that the bridge is about 15 miles northwest of Peshawar.

A NATO spokesman in Afghanistan confirmed that 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....

It was not immediately clear whether supply convoys could reach Afghanistan through alternative routes in the region, nor how long it would take to rebuild it.

The Khyber Pass is one of two routes into Afghanistan from Pakistan, according to Reuters. The other connects the Pakistani province of Baluchistan with the southern Afghan city of Kandahar.

While the military provides few specifics of its supply operation, observers believe most of the supplies travel through the Khyber Pass, says Reuters.

The U.S. military and NATO have not given details of the supplies they get via Pakistan or a breakdown of how much comes on the two routes. The U.S. Defense Department says the U.S. military sends 75 percent of supplies for the Afghan war through or over Pakistan, including 40 percent of fuel.

Pakistani customs officials say under normal circumstances about 300 trucks with Western force supplies travel through the Khyber Pass crossing at Torkham every day, compared with about 100 through the Chaman crossing.

With the US planning to expand its Afghan operations, Tuesday's bridge attack highlights the need for secure supply routes. US planners say they are actively looking for routes that avoid Pakistan's volatile border areas.

There are 36,000 American soldiers currently stationed in Afghanistan, where they are training Afghan security forces and doing battle with a Taliban insurgency against the government of US ally Hamid Karzai.

There are plans to add as many of 30,000 additional troops to that total, reports Agence France-Presse. Last week, US Defense Secretary Robert Gates indicated that as many as 12,000 could be in place by summer.

Reuters reports that US Central Command chief David Petraeus said last month that NATO had reached an agreement to transport supplies into northern Afghanistan through Russia and Central Asia, but would not provide specifics. Probable routes would bring supplies through Kazakhstan, Turkmenistan, and Uzbekistan.

The bridge bombing follows more than a week of heavy bloodshed in Pakistan's increasingly lawless northwest that has claimed more than 80 civilian lives in nine days, according to the BBC.

Fighting has been focused on the Swat Valley, where Al Jazeera reports that more than 20,000 people have fled their homes due to fighting.

Wajid Ali Khan, a provincial minister, has said "the fighting in the valley has made it almost impossible for civilians to stay there".

Government forces and other state employees are bearing the brunt of many attacks by Fazlullah loyalists, Kamal Hyder, Al Jazeera's correspondent in Pakistan, said.

The decapitated bodies of policemen - complete with notes warning the authorities of further such attacks - have become a common sight on streets in Swat, Hyder said.

The Pakistani military says it killed 35 Taliban-allied militants in overnight fighting on Monday, according to the BBC. Local residents say more than 40 civilians were killed in the crossfire between government forces and insurgents.

Also on Monday, John Solecki, a US official with the UN High Commission for Refugees, was abducted while on his way to work in Quetta, the capital of Baluchistan Province.

The New York Times reports that he is the first Westerner targeted in the city in recent memory. Baluchistan is home to several separatist groups with no history of attacks on foreign targets, but the province also has a small Taliban presence. While the identity of Solecki's abductors is so far unclear, they are believed to be Taliban.