Twenty-seven people have been killed in a suicide car bomb attack at a meeting of tribal elders in a restive region of Pakistan near the Afghan border.
Eighty-one people were injured, many of them critically, in the blast in the Orakzai semi-autonomous tribal region.
The bomber struck as some 600 people held an open-air meeting to raise a militia to evict Taleban from the area.
In recent weeks, tribesmen in the north-west have taken up arms to fight the Taleban alongside Pakistani troops.
Orakzai, near the main north-west city of Peshawar, has been relatively calm in recent months.
But other parts of the north-west have seen sustained military operations by Pakistani troops against militants in the regions of Bajaur and Swat.
There has also been an upsurge in cross-border attacks against suspected militant targets in Pakistan by US forces in Afghanistan.
Pakistan says these are undermining its efforts in the "war on terror".
Those present at Friday's meeting in Orakzai said the suicide bomber drove his car into the gathering and blew himself up.
"We were busy raising a lashkar [tribal militia] to evict Taleban from the region when this attack took place," Qeemat Khan Orakzai, a member of the council, told Reuters news agency.
"I fell down unconscious. When I woke up, I saw dead and wounded around me."
A security official told AFP news agency: "The tribesmen blew up two hideouts of the militants a day earlier and it is possible this attack was in revenge for their actions."
The attack also comes a day after the Taleban claimed responsibility for a suicide bombing of a building belonging to an anti-terror squad in the capital Islamabad's main police complex.
Pakistani troops want tribesmen to help them fight the militants
They are also suspected to have been behind a roadside bombing in Dir in North West Frontier Province which killed at least 10 people, four of them schoolgirls.
Pro-Taleban militants on the Pakistan side of the border have been blamed for a rise in attacks on US and Nato troops in Afghanistan.
The Taleban has killed dozens of tribal elders they accuse of backing the government in recent years.
America has increased strikes in Bajaur and other tribal areas on the Afghan border, targeting suspected militants.
The Pakistani army has denounced the raids. It fears they will make the tribes switch sides, and turn the emerging anti-Taleban sentiment into an anti-American one.
"We want them [the US] to realise that these attacks are destabilising the situation, and they are not helping them or Pakistan," foreign ministry spokesman Mohammed Sadiq said on Friday.
"They are helping the terrorists."