But it was unclear if the detentions at a religious school in the North West Front province were related to the blast.
Friday's bombing, apparently targeting Aftab Khan Sherpao, the former interior minister, was the second such attack on him in eight months.
No strong leads
Sharif Virk, the provincial police chief, said that so far forensic evidence at the site of the blast was insufficient to give up any strong leads.
"No head has been found from the scene," he said, referring to the fact that the heads of suicide bombers are often blown off by the force of the explosions and later found intact.
"We have found four legs which we have sent for DNA test, but it could be little help unless we know the family."
Virk said the attack could be linked to armed groups in the adjacent Mohmand tribal region.
The attack sparked anger and fears of further attacks should Pakistani forces crackdown on tribal fighters.
Fawad Khan, relative of a blast victim, said: "Why did these people, the government, spoil the situation in Swat, Bajaur and the Red Mosque? Now that they have done so, naturally even those people the militants are going to retaliate."
Kamal Hyder, Al Jazeera's correspondent in Pakistan, said: "It was widely expected that there would be attacks against Aftab Khan Sherpao ... he had been warned there would be revenge attacks."
Besides being blamed for a security crackdown on armed tribal groups, many hold Sherpao personally responsible for the assault on a hardline mosque in Islamabad in July.
Shortly after the bombing, Robert Gates, the US defence secretary, said that al-Qaeda had "re-grouped" along the Afghan-Pakistan border and begun to focus attacks on the Pakistani government and military,
Suspicion for the blast was expected to focus on pro-Taliban and al-Qaeda fighters active in the North West Frontier Province.
Pervez Musharraf, Pakistan's president, condemned the blast and directed security and intelligence agencies to track down the masterminds, the state-run Associated Press of Pakistan reported.
|Scores of civilians were also injured in|
the attack [Reuters]
The UN and US also condemned the attack.
Sean McCormack, a US state department spokesman, said: "Violence for political gain is never justified, and is even more disturbing during such a special holiday in the Islamic faith."
Tariq Azeem Khan, a Pakistani senator, told Al Jazeera: "I think that this is a direct fallout from what is happening in Afghanistan and our own position on the war on terror.
He said more such attacks may be a possibility in the run-up to elections.
Imtiaz Gul, a political analyst, told Al Jazeera that the message from the attack was "that all those people associated with the war on terror, the policy makers, the decision makers, and those who are involved in the implementation, they are the obvious targets of the militants".
"Only political dialogue with the militant forces or these who support these forces perhaps could bring about any change and contain these attacks."
Source: Al Jazeera and agencies