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.
The latest attack took place early in the afternoon in the town of Alpurai, in Swat valley in Shangla district.
Syed Shoaib Hasan, BBC News, Islamabad
While most of Swat's territory, especially its urban areas, is firmly in the control of the army, recent attacks suggest that the militants are not completely routed.
But that is something the military itself has admitted, saying that Swat's rural areas are still a source of trouble. However, they remain confident that the situation will soon be under control.
This does leave a big question mark over the South Waziristan operation. While the political leadership has been talking about destroying the militants in their main stronghold, the military has firmly kept itself aloof from any such adventure.
But with the militants striking back hard, a national consensus seems to be pushing them towards launching an all-out operation. With winter around the corner, the military will have to move soon if it aims to achieve this. At the moment though, the initiative lies with the militants.
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.
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.
ATTACKS IN PAST WEEK
12 October: 41 killed in bombing in Alpurai
10-11 October: 19 killed in raid on army HQ, Rawalpindi
9 October: 49 killed in bombing in Peshawar
5 October: Five killed in suicide blast in UN's Islamabad office
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