Two suicide bombers dressed in burqas struck a crowd of displaced people collecting aid handouts, killing at least 32 and wounding more than 50 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.
"The toll in the two suicide attacks is 32 dead and more than 50 wounded," local police chief Dilawar Khan Bangash told AFP by telephone from the scene.
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.
"The two tribes raised a lashkar (tribal militia) to fight Taliban in Orakzai," he said adding that security forces suffered no casualties.
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.
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.
Pakistan's latest military offensive and ongoing extremist violence have displaced at least 210,000 people from the tribal districts of Orakzai and Kurram, most of whom have registered in Kohat and Hangu towns.
On Saturday, army chief of staff, General Ashfaq Kayani, made a rare public apology over the "unfortunate" deaths of civilians during military action last week in the Khyber tribal district.
Military officials initially said at least 42 militants were killed in a gunfight and two air strikes in the Tirah valley, but tribesmen later said dozens of civilians were killed last Saturday.
Northwest Pakistan suffers from chronic insecurity largely connected to the neighbouring 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.
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.
Last year, a total of 3.1 million people were displaced from their homes in Pakistan's North West Frontier Province and the semi-autonomous Federally Administered Tribal Areas along the Afghan border.
Nearly two million people have returned home, but uncertainty continues in the wake of ongoing clashes between troops and the Taliban.
Jean-Maurice Ripert, the UN special envoy in charge of humanitarian affairs for Pakistan, last week pressed donors for urgently needed funds for the displaced amid warnings that some aid projects may have to be cut.
On Monday the UN humanitarian coordinator for Pakistan, Martin Mogwanja, said that the world body had so far received only 106 million dollars from the donors, barely 20 percent of a total appeal for 537 million dollars.
Orakzai, the current focus of Pakistani military operations, is a former bastion of Tehreek-e-Taliban Pakistan leader Hakimullah Mehsud, whom US officials believe probably died in a US drone attack in January.