Fifteen Pakistani soldiers were killed and 25 wounded when their convoy was hit by a roadside bomb in the northern district of Swat today, police said.
The explosion set fire to a truck loaded with ammunition, and state television reported a firefight then broke out. The attack came a day after the military sent around 2,000 troops to the district in response to growing militant activity.
Militants have attacked security forces and carried out bomb attacks in recent months in the North West Frontier Province, and have been forcing residents there to follow a strict Islamic code.
Pakistani tribal areas have been a hotbed of support for al-Qaeda and Taliban militants who have fled Afghanistan.
Violence has grown across Pakistan since July, when militants scrapped a peace deal and the army raided a radical mosque in the capital, Islamabad.
At least 139 people were killed in a suicide attack on a procession led by former prime minister Benazir Bhutto in Karachi last week on her return from eight years of self-imposed exile.