A homicide bomber blew himself up Sunday at a large meeting called by tribal elders pushing for peace in northwestern Pakistan, killing at least 40 people and injuring more than 100, witnesses and officials said.

It was the third suicide bombing in as many days in the volatile northwest, where security forces were battling pro-Taliban Islamic militants.

Thousands of people were at the meeting in Darra Adam Khel in North West Frontier Province about 25 miles south of the provincial capital, Peshawar. The five tribes involved wanted to finalize a resolution calling for punishing anyone who sheltered or helped militants, including those of Al Qaeda and the Taliban, Interior Ministry spokesman Javed Iqbal Cheema said on state-run Pakistan Television.

Alam Khan, a tribesman who attended, said a young man walked up to a group of elders and blew himself up.

"It was a huge explosion and left body parts and blood scattered on the ground," said Ramin Khan, whose left leg and face were wounded.

President Pervez Musharraf said the attack was an attempt to sabotage the peace process and reiterated the government's "resolve and commitment" in the fight against terrorism and extremism.

Dr. Hamid Afridy, the area's chief medical officer, said he counted 40 bodies, some with severed limbs and mutilated faces, at the site.

"We have dispatched more than 100 injured to .. hospitals" in Peshawar and Kohat town, he told The Associated Press. He said he feared the death toll could rise because many of the injured were in critical condition.

Pakistan Television said the suspected bomber's severed head was found.

Television footage showed blood, shoes and caps littering the bombing site — a tree-lined ground amid wheat fields that is only a few yards away from brick homes.

On Friday, a suicide bomber blew himself up at the funeral of a slain police officer in Mingora town in Swat Valley, killing more than 40 people and injuring at least 60. The next, day 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, an apparent reflection of how Musharraf's government has lost control of parts of the region.

Meanwhile, a prominent opposition lawyer who had been under house arrest since Musharraf declared a state of emergency more than three months ago was freed Sunday, police said.

The attorney, Aitzaz Ahsan, said the police who had been restricting him to his home in Lahore have left.

Ahsan, a strong critic of the president, had been under house arrest since Nov. 3, when Musharraf declared a state of emergency and fired dozens of independent-minded judges, including the country's Supreme Court justices, who had been expected to rule on the legitimacy of his October re-election.

Ahsan, who is president of the Supreme Court Bar Association, has been at the forefront of demands that Musharraf reinstate the justices. Hours after being freed he led a rally of lawyers and called for the judges to be reinstated.