Five tribes were meeting to finalize a resolution that would punish anyone who shelters or helps Islamic militants, including al-Qaida and Taliban fighters, Interior Ministry spokesman Javed Iqbal Cheema said.
A young man walked up to a group of elders and detonated his explosives, said Alam Khan, a tribesman at the meeting in Darra Adam Khel, a town in North West Frontier Province about 25 miles south of the provincial capital, Peshawar.
"It was a huge explosion and left body parts and blood scattered on the ground," said Ramin Khan, another participant whose left leg and face were injured. He and others hurt in the attack were brought to a hospital in Peshawar.
Dr. Hamid Afridy, the area's chief medical officer, said he counted 40 bodies and more than 100 injured were sent to the hospital. He said many were in critical condition and feared the death toll could rise.
Television footage showed blood, shoes and caps littering the bombing site - a tree-lined ground surrounded by wheat fields and only yards away from brick homes.
Musharraf called the bombing an attempt to sabotage tribal efforts to rid the region of militant influence and reiterated the government's "resolve and commitment" in the fight against terrorism.
The attack came two days after a suicide bomber struck at the funeral of a slain police officer in Mingora town in Swat Valley, killing more than 40 people and injuring at least 60. On Saturday, another suicide bombing in nearby Bajur killed one person and wounded 19 others, mostly security personnel.
Friday's bombing was the bloodiest attack in the Swat Valley since militant followers of a pro-Taliban cleric, Maulana Fazlullah, grabbed control of large parts of the scenic corner of Pakistan's restive northwest.
The army says it has retaken most of Swat since Musharraf sent thousands of troops in November, but attacks persist and Fazlullah remains at large.
Musharraf has U.S. backing for his support in battling Taliban and al-Qaida militants, many of whom operate in rugged parts of Pakistan near the Afghan border.
But the Pakistani president has faced an uncertain political future since his allies were soundly defeated in parliamentary elections last month. His popularity plummeted last year after he declared a state of emergency, clamped down on the media and fired dozens of independent-minded judges, including the Supreme Court justices.
On Sunday, a prominent lawyer who has led demands that Musharraf reinstate the justices was freed from house arrest, a possible sign the government was softening its stance toward critics.
Aitzaz Ahsan, the president of the Supreme Court Bar Association, said police who had been restricting him to his home in Lahore have left. Hours after being freed, he led a rally of lawyers calling for the judges to be reinstated.
Ahsan was first arrested during last year's crackdown. He was released for two days earlier this year and then put back under house arrest.
Ahsan belongs to the Pakistan People's Party of slain former Prime Minister Benazir Bhutto. The party won the most seats in the Feb. 18 parliamentary elections and has vowed to try to curb Musharraf's power.
--- Associated Press reporters Zarar Khan and Sadaqat Jan in Islamabad contributed to this report.
