Two suicide bombers struck outside a government office Friday in a tribal region where Pakistan's army has fought the Taliban, killing more than 50 people and wounding more than 100, officials said.
The attack, one of the deadliest in Pakistan this year, indicated that militants remain a potent force in the country's tribal belt bordering Afghanistan despite army offensives against them.
The U.S. has praised Pakistan for taking on Islamist extremists that use the tribal region to plan attacks on Western troops across the border, but the militants have often retaliated on Pakistani soil.
The bombers detonated their explosives near the Yakaghund village office of Rasool Khan, a deputy administrator of the Mohmand tribal region who escaped unharmed. At least one bomber was on a motorcycle.
Nearby, officials were distributing wheelchairs to disabled people and equipment to poor farmers, said Mohmand's chief administrator, Amjad Ali Khan. He said more than 50 people were killed and more than 100 were wounded.
One of the bombs appeared fairly small but the other was huge, and they went off within seconds of each other, Amjad Ali Khan told The Associated Press.
Some 70 to 80 shops in the area were damaged or destroyed, Rasool Khan said. A prison building also was damaged, and some 28 prisoners - ordinary criminals, not militants - had apparently escaped, he said.
Video footage from the area showed dozens of men searching through piles of yellow brick and mud rubble in search of survivors.
"After the blast, I saw destruction. I saw bodies everywhere. I saw the injured crying for help," security official Esa Khan told The Associated Press in the main northwest city of Peshawar, where he helped escort some of the wounded to a hospital.
Abdul Wadood, 19, was sitting in a vehicle nearby when the attack happened.
"I only heard the deafening blast and lost consciousness," he said while being treated for head and arm wounds in Peshawar. "I found myself on a hospital bed after opening my eyes. I think those who planned or carried out this attack are not humans."
Mohmand is one of several areas in Pakistan's lawless tribal belt where Taliban and al Qaeda members are believed to be hiding. The Pakistani army has carried out operations in Mohmand, but it has been unable to root out the militants.
Information from Mohmand is difficult to verify independently because access to the area is heavily restricted.
The attack occurred as U.S. Sens. Carl Levin, chairman of the Senate's Armed Services Committee, and Jack Reed, a committee member, met with Pakistani officials in Islamabad.
In a statement issued after he met the American lawmakers, Pakistani Prime Minister Yousuf Raza Gilani said both countries should try harder to increase mutual trust.
He said Pakistan was doing its utmost to combat militancy, and "expected friendly countries like (the) U.S. to share with it credible and actionable information rather than indulging in blame game, in order to achieve our shared and common goal of succeeding against militancy."
Over the past decade Pakistan and the U.S. have frequently questioned each other's motives in the region.
Pakistan has been suspected of fomenting problems in Afghanistan as a part of its regional struggle with India, while Islamabad has suggested that Washington gives favorable treatment to New Delhi in areas such as nuclear armament.
In a reference to its larger archrival, Gilani said the U.S. should take a "fair and nondiscriminatory approach ... in its relations with the regional countries."
In recent visits to Pakistan, U.S. officials have stressed that the relationship between the two countries has improved.