PESHAWAR, Pakistan - Police examined clothing, shoes and the severed legs of a man yesterday to try to identify a suicide bomber who killed at least 50 people during a holiday prayer service at a crowded mosque in northwestern Pakistan.

Security officers arrested seven students from an Islamic school hours after the blast Friday, which apparently targeted former Interior Minister Aftab Khan Sherpao, who had been deeply involved in Pakistan's fight against militants linked to the Taliban and al-Qaeda.

The bomber struck a mosque inside the politician's residential compound in the village of Sherpao during prayers for the Islamic holy day of Eid al-Adha.

Sherpao escaped harm, but one of his sons was wounded, and at least 50 people were killed. The former minister had survived a suicide attack at a rally in the nearby town of Charsadda eight months ago that killed 28 people. Officials blamed al-Qaeda for that attack.

Suspicion for the blast was expected to focus on the pro-Taliban or al-Qaeda militants active in northwestern Pakistan, near the Afghan border. The attack also deepened the sense of uncertainty in Pakistan ahead of Jan. 8 parliamentary elections. Sherpao, head of the Pakistan Peoples Party-Sherpao, is a candidate.

Police collected pieces of clothing, shoes, prayer mats and two severed legs of a man from the scene of Friday's bombing, and investigators were examining them for clues to identify the bomber, an official involved in the probe said.

The raid of the Islamic school in the nearby village of Turangzai was carried out based on intelligence information, a second police official said.

Pakistani President Pervez Musharraf condemned the blast and directed security and intelligence agencies to track down the masterminds, the state-run Associated Press of Pakistan reported.

The bomber was in a row of worshipers when he detonated the explosive, provincial police chief Sharif Virk said Friday. Witnesses said the dead included police officers guarding Sherpao, who was praying in the mosque's front row at the time of the attack.

As interior minister, Sherpao oversaw one of Pakistan's civilian spy agencies, police and paramilitary forces involved in operations against militants along the Afghan border.

He was a longtime supporter of former Prime Minister Benazir Bhutto's Pakistan People's Party before defecting and joining the government after the last parliamentary elections in 2002. He left office last month.

Taliban and al-Qaeda fighters have extended their influence over tracts of Pakistan's volatile northwest in the last two years and in recent months have launched numerous suicide attacks.

The army says the most recent attacks could be retaliation for a military operation against militants in the Swat valley, where it says it has killed about 300 militants since last month.

The violence came as Pakistan struggled to emerge from months of political turmoil.

Musharraf recently declared emergency rule for six weeks, a move that he said was necessary to combat rising Islamic extremism but that was widely seen as a ploy to prolong his own presidency.

Meanwhile, police said yesterday that three suspected Pakistani militants, carrying explosives in a car, were arrested during routine security checking on a road from the North West Frontier Province to the eastern province of Punjab.