(BBC) - At least 17 Pakistani soldiers and a number of civilians have been killed in an attack on an army vehicle in the northern region of Swat.
The attack comes one day after the army deployed 2,500 more troops in the area to combat rising militancy.
More than 35 people were taken to hospital for treatment.
The Swat valley in North West Frontier Province has become a stronghold of an anti-government militant leader, Maulana Fazlullah.
He has reportedly used radio broadcasts to call for jihad, or holy war, against the Pakistani authorities.
There has so far been no claim of responsibility for the attack.
The army vehicle, carrying munitions, exploded in the attack in Mingora, the main town in the district of Swat.
Most reports indicate that the blast was caused by a roadside bomb.
"It was a huge explosion. Then the truck was on fire," student Taj Mohammed Khan said, the Associated Press news agency reports.
"There were flames, smoke and people crying. People were scared to go near because bullets were going off."
Some reports say that as many as 30 soldiers and civilian bystanders were killed.
"The blast was so powerful that that it destroyed 10 shops and hit a three-wheeler (rickshaw) killing all the passengers inside it," Swat Mayor Fazlur Rehman told the AFP news agency.
Dr Asadullah of the Saidu Sharif hospital in Mingora said 18 bodies had been brought in, many of them charred by the blast and fire that erupted afterwards.
At least 35 injured people were being treated by hospital staff, he said.
A local journalist at the scene told the BBC the death toll could be higher because many dead bodies of civilians were not taken to the hospital.
He said about 45 paramilitary troops were sitting in the truck when it was hit by an improvised explosive device planted on the road side.