Pakistan launched an offensive in Bajur three months ago to dismantle what it said was a virtual Taliban mini-state that is a source of militants flowing into Afghanistan.
The Salarzai tribesmen were preparing to stage an assault on local militant hide-outs when the blast occurred, said Iqbal Khattak, a government official. Malik Rahimullah, a tribal elder, said the bomb exploded as soon as armed contingents began to move.
He and officials initially said it appeared that a remote-controlled bomb was used, but later Khattak said mutilated body parts of an apparent suicide bomber were found, and that witnesses said they saw a young man rushing into the crowd before the explosion.
Amir Khan, a tribesman, said the scene was littered with severed limbs and that several tribal elders were among the dead.
Khattak said nine people were killed. Mohammad Kareem, a hospital official in Bajur's main city of Khar, said two dozen of the wounded were in serious condition.
The army claims to have killed some 1,500 insurgents in its offensive. At least 73 troops and 95 civilians have also died, it says. Lack of security and government restrictions make verifying accounts of the fighting impossible.
U.S. officials praise the operation in Bajur, saying it has reduced violence on the other side of the border. The U.S. has long been concerned that pockets of Pakistan's northwest are sanctuaries for militants involved in attacks on American and NATO forces in Afghanistan.
Militants have responded to the military offensives - as well as stepped-up U.S. missile strikes in parts Pakistan's border zone - with a wave of suicide attacks that are adding to concern about the U.S.-allied country's stability.
The militants also have gone after the tribal militias, including beheading some of the elders involved. A suicide attack in October in the nearby Orakzai tribal region against another such militia left dozens dead.
On Wednesday, an airstrike killed 15 suspected militants in Airab village in Bajur, according to Jamil Khan, a senior government official. He said the 15 dead included a Pakistani militant commander named Wali Rehman. Khan said Rehman was known to shelter foreign militants linked to al-Qaida.