Hyder said that local reports were saying that two security forces personnel and four civilians were among the dead. 
Local television footage showed a car enveloped in flames and black smoke billowing down a street, as casualties lay on the ground.

"I was going for some work in the bazaar but was stopped by security forces because the army convoy was moving," Saeedur Rehman, a teacher, told the AFP news agency.

"Suddenly there was a huge blast and smoke filled the area. Then heavy firing started and I lay on the ground."

'Inhuman acts'

Yusuf Reza Gilani, Pakistan's prime minister, condemned the bombing, vowing that "such inhuman acts of terrorism" would not sway Pakistan from its determination "to curb this menace and fight the insane extremists".

More than 3,000 people have been killed in suicide attacks and other bombings across Pakistan since July 2007.

Pakistani forces staged a military offensive in North West Frontier Province last year in an attempt to retake the region from Taliban control.

In July, after two months of fighting that left an estimated 2,150 fighters dead, the army said it had largely cleared the Taliban from Swat and neighbouring Buner and Lower Dir.   

General James Jones, the US national security adviser, visited Swat earlier this month and congratulated Pakistani security forces on the "success" of their operations and noted their  "tremendous sacrifices".
But despite the relative calm, sporadic clashes and suicide attacks continue to rock the valley.