Two suicide bombers dressed in burqas struck a crowd of displaced people collecting aid handouts, killing at least 41 and wounding more than 60 on Saturday at a camp in northwest Pakistan.
The bombers struck minutes apart in the Kacha Pukha camp on the outskirts of the garrison city of Kohat, a registration centre for people fleeing Taliban violence and Pakistani army operations close to the Afghan border.
The attacks underscored the grave threat posed by extremists despite stepped-up Pakistani offensives and a significant increase in US drone attacks targeting Taliban and Al-Qaeda-linked commanders in the nearby tribal belt.
"We have 41 dead in the twin suicide bombing. There are 64 injured," local police chief Dilawar Khan Bangash told AFP by telephone.
He said the bombers walked into the crowd wearing burqas, the loose-fitting head-to-toe outfit that obscures the face and worn by conservative Muslim women in parts of northwest Pakistan and Afghanistan.
Body parts of the bombers were recovered and most of the victims were members of the Mani Khel and Baramad Khel tribes who had gathered for registration after fleeing fighting in their home district of Orakzai, he said.
Bangash said the first bomber detonated his explosives while displaced people gathered to register and receive relief items. A few minutes later the second bomber blew himself up in the middle of the gathering crowd.
Khalid Omarzai, the local chief of administration, also said 41 people died, including Azmat Ali Bangash, a journalist working for local TV channel Samaa.
Northwest Pakistan has suffered a major internal displacement of people as a result of Taliban violence and a series of military offensives concentrated on flushing out the armed Islamists from parts of the northwest and tribal belt.
The United Nations says 1.3 million people are currently displaced.
At least 210,000 people have been displaced from the tribal districts of Orakzai and Kurram, most of whom have registered in Kohat and Hangu towns.
Under US pressure, Pakistan has in the past year significantly increased operations against militants in its tribal belt, which became a stronghold for hundreds of extremists who fled Afghanistan after the 2001 US-led invasion.
On Saturday army chief of staff General Ashfaq Kayani made a rare public apology over the "unfortunate" deaths of civilians during air strikes in Khyber, part of the tribal badlands, last Saturday.
Military officials initially said 42 militants were killed in a gunfight and two air strikes in the Tirah valley, but tribesmen later said up to 61 civilians were killed. A security official estimated that 15 civilians died.
One elder in the Khukikhel tribe accepted the apology but said those responsible should be punished.
Northwest Pakistan suffers from chronic insecurity largely stemming from the semi-autonomous tribal belt, which Washington calls the most dangerous place on Earth and a global headquarters of Al-Qaeda.
A campaign of suicide and bomb attacks have killed more than 3,200 people in less than three years across the nuclear-armed country of 167 million, blamed on Al-Qaeda, Taliban and other extremist Islamist groups.
On Friday, a suicide bomber blew himself up at the main hospital in the southwestern city of Quetta, killing 10 people, in what police said was a sectarian attack linked to the shooting of a Shiite banker.
Last year, 3.1 million people were displaced from their homes in northwest Pakistan. Nearly two million people have returned home, but uncertainty continues in the wake of ongoing clashes between troops and the Taliban.