A suicide bomber on a motorbike killed at least 56 people, including women and children, in an attack in a volatile Pashtun region on the Afghan border on Friday, officials said.
The bomber blew himself up as hundreds of people were gathered around the office of a senior government official in Pakistan's northwestern Mohmand region, where security forces have stepped up attacks on Taliban militants in recent weeks.
"The death toll has risen to 56. It could be more as people are still pulling out people trapped in the rubble of fallen shops," Rasool Khan, the region's assistant political agent, told Reuters. The attack took place outside his office.
Hospital officials said nearly 80 people were wounded, while government officials put the number at about 50.
Among the wounded were several people displaced by fighting between security forces and militants, who were collecting relief goods near the blast site. Residents said five children, aged between 5 and 10, and several women were among dead.
"I was standing about 200 yards (metres) away from the office when I heard the blast. I don't know how it happened but I could see several bodies lying on the ground after the explosion and people running in all directions," said Riaz Hussain, a witness.
Television footage showed victims being pulled out of the debris. The blast also damaged several cars and about 30 shops, witnesses said.
A security official at the scene said the blast also damaged a nearby prison wall and several inmates had escaped.
Pakistan launched two major offensives in the northwest last year against homegrown Taliban militants who have killed hundreds of people in retaliatory attacks across Pakistan, mostly in the northwest, but also in major cities.
Two suicide bombers killed at leat 42 people in an attack on Pakistan's most important Sufi shrine in the eastern city of Lahore last week.
The Pakistani Taliban, allies of the Afghan Taliban, have lost ground in army offensives over the past year.
They were pushed out of the Swat valley, northwest of Islamabad, and in October the army began an offensive in the militants' South Waziristan bastion on the Afghan border.
The offensive was extended to Orakzai in March as many of the militants who fled the South Waziristan operation took refuge there and in Mohmand. Hundreds of militants have since been killed in air strikes in the two regions.
Jet fighters killed about a dozen militants in attacks in Orakzai on Friday, security officials said. There was no independent verification of the casualties as militants often dispute and reject official figures.