Pakistani police are hunting for clues as to who was behind a suicide bombing that killed some 50 people at a mosque near the north-west city of Peshawar.
Security officials said the bomber was among the congregation
Forensic scientists have been combing the remains of the explosive device and the victims, who were part of a large crowd offering prayers for Eid al-Adha.
An Islamic school in a nearby village was also raided and seven students arrested, reports say.
Former Interior Minister Aftab Sherpao was in the congregation but was unhurt.
It was the second suicide bombing in eight months apparently targeting Mr Sherpao - a close ally of President Pervez Musharraf.
The violence comes as Pakistan prepares for a general election next month.
Worshippers at the mosque in the Charsadda district of North West Frontier Province were celebrating Eid al-Adha, the Festival of Sacrifice, when the suicide bomber blew himself up amongst the 1,000-strong crowd.
Police said the bomb contained 6-8kg (13-17lb) of explosives and was packed with nails and ball bearings to maximise casualties.
"There was blood and body parts everywhere... People were running. Some people were injured in the chaos," said Iqbal Hussain, a police officer in charge of security at the mosque.
Mr Hussein said he did not know how the bomber managed to gain entry to the mosque because the congregation had been forced to pass through metal and explosive detectors.
After the victims and dozens of wounded were removed from the mosque complex, police and forensic scientists began carefully sifting through the rubble, as well as the bloody shoes and clothes left behind.
There has been a wave of suicide bombings in the past six months
President Musharraf later issued a statement ordering the security forces to "track down the masterminds behind this abhorrent act".
"No Muslim could even think of committing such a heinous crime," he was quoted as saying by the Associated Press of Pakistan news agency.
"A handful of extremists were bent upon forcing their way of distorted thinking on the vast majority of moderate and practicing Muslims, which was totally unacceptable," he added.
Dozens of security officials later raided an Islamic school in a nearby village and arrested seven students, the Associated Press reported - although officials would not say if the raid was connected to the bombing.
Islamist militants suspected
The BBC's Barbara Plett in Islamabad says the likeliest suspects are pro-Taleban militants, who have stepped up attacks against the government in retaliation for operations against them in the border areas near Afghanistan.
More than 600 people have been killed during the past six months, including about 200 soldiers, in violence sparked by the ousting of armed militants from the radical Red Mosque in Islamabad in July.
As interior minister in the government recently dissolved by Mr Musharraf ahead of the 8 January election, Mr Sherpao was the country's top security official and led the campaign against militants.
The threat of growing Islamist violence was cited by Mr Musharraf when he declared a state of emergency in Pakistan last month. He ended emergency rule last Saturday, however, saying the threat had been contained.
US Defence Secretary Robert Gates said in the wake of the latest bombing that al-Qaeda had "re-established itself" in the border areas and begun to focus on attacking the Pakistani government.
"Al-Qaeda seems to have turned its face toward Pakistan and attacks on the Pakistani government and Pakistani people," he said.