Devastation in the town of Alpurai following the blast
At least 41 people have been killed in a suspected suicide car bombing in Pakistan's Swat valley, officials say.The explosion hit a security convoy in Shangla district - an area the military said it had retaken from militants.
It is the latest in a string of attacks and comes amid warnings of an offensive against militants in nearby South Waziristan, on the Afghan border.
On Saturday militants stormed the army headquarters in Rawalpindi. Pakistan vowed to hit back "imminently".
The Pakistani Taliban said it had carried out the attack in Rawalpindi, through a Punjab faction of the group.
Spokesman Azam Tariq said it was to avenge the recent killing of Pakistani Taliban leader Baitullah Mehsud by a US drone.
Dozens hurt
The latest attack took place early in the afternoon in the town of Alpurai, in Swat valley in Shangla district.
Alpurai was not under Taliban control at the time of a major anti-Taliban offensive by the military in Swat valley earlier this year.
Security officials say a car blew up near a hospital in the market as a convoy of troops was passing by.
Dozens of people, including security personnel, are said to have been injured in the explosion.
"It appears to be a suicide attack," Reuters news agency quoted Shangla police official, Khan Bahadur Khan as saying.
"The bomber hit one of three military vehicles that were passing through the busiest market in the district," he said.
Witnesses said the area was strewn with debris. A military spokesman said several trucks were destroyed in the blast.
The bombing - the fourth major attack within a week - brings to over 100 the death toll in four days of militant attacks across Pakistan.
Bajaur bombardment
Earlier on Monday, Pakistani security forces used aircraft and artillery to bombard militants in the Bajaur tribal district near the Afghan border.
A security official told the BBC at least 15 militants were killed and over 25 injured in the raids on hideouts.
But local tribesmen told the BBC at least five of those killed were civilians, including women and a child.
The bombardment began after the end of a deadline for local Taliban militants to lay down weapons.
In June the army declared the three-month anti-Taliban offensive in the Swat valley a success.
It has arrested several high-profile Taliban leaders in Swat since then, including the spokesman for the Taliban in Swat, Muslim Khan.
Muslim Khan's capture was viewed as a major coup against the Taliban, although the group's leader in Swat, Maulana Fazlullah, remains at large.
More than a million people were displaced by the Swat offensive. Many have since returned and the army maintains a significant presence there.
Some analysts say that in the wake of the army onslaught a number of militants fled to neighbouring districts.
During the offensive, fighting also spilled into Shangla district.
Over the past few months troops have also been gathering on the border of South Waziristan, where the Taliban have one of their main strongholds.
After Baitullah Mehsud was killed by a US missile in early August, there was a relative lull in Taliban attacks.
But there has been a resurgence in militant activity since the start of this month.
