Suspected militants in north-western Pakistan have blown up a bridge, cutting a crucial supply link to Nato forces in neighbouring Afghanistan.
Most supplies for the international forces in Afghanistan come through the Khyber Pass in Pakistan.
The US army has been setting up other supply routes to counter the increasing attacks on the road between Peshawar in Pakistan and Afghanistan.
Meanwhile, fierce fighting is said to be continuing in the Swat valley.
The army says in the past two days it has killed at least 35 militants behind a campaign to enforce Taleban-style Islam. Local residents say the number of civilians killed in the valley since the weekend has risen to 40.
The bridge in the Khyber district was blown up at 0600 local time (0100 GMT) and all traffic on the road had been suspended, news agency AFP quoted key official, Tariq Hayat, as saying.
"We are sending teams to repair the bridge and restore the traffic flow," he said.
The 30-metre (100-foot) iron bridge is 23km (15 miles) west of Peshawar.
Convoys on the winding mountain road between Peshawar and Afghanistan have been increasingly targeted.
In December, many truck drivers in Pakistan refused to continue delivering supplies following a series of hijackings by suspected Taleban militants in the area.
The attacks led the US to announce it had agreed with Russia and other states an alternative supply route through Central Asia.
In Swat, local residents say there is intense fighting in the Matta and Kabal areas.
On Monday, Pakistan's army said it had retaken high ground from the militants in the Charbagh area near Mingora, the main town in the Swat valley.
The area has been the scene of a major battle since Saturday.
The clash is the latest in an operation against an increasingly powerful Taleban insurgency in the valley.
The military launched its offensive last week in response to a public outcry over the Taleban's growing strength in Swat.
The militants have tightened their hold on the valley, banning girls' education, setting up their own courts and killing those they oppose, sometimes beheading their victims.
As many as 80 civilians have been killed in the area over the past nine days, BBC Urdu service reports, quoting local sources.
The army says it has killed 35 militants in two days of fighting in the Charbagh, Ali Grama and Manglawar areas, but there is no independent confirmation of the claim.
Witnesses say most of the people killed are civilians.
The army does not deny civilian casualties, but says it often has no way of identifying the militants from the civilian population.
Most areas in the upper Swat region remain under curfew and, as a result, bodies are lying unattended in several houses hit by artillery shells or bombs dropped from helicopter gunships, residents say.
They say a large number of people have become homeless but they cannot get out of the area due to the curfew and fighting.
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