LAHORE, Pakistan (CNN) -- Police raided an Islamic school and arrested seven students hours after a blast in a mosque in northern Pakistan left at least 50 dead and dozens injured, according to an Associated Press report.
A man, right, mourns the death of his two sons in a suicide attack near Peshawar that killed at least 50.
A bomb, packed with ball-bearings and nails, tore through Eid prayers at a mosque packed with hundreds of worshippers northeast of Peshawar on Friday, targeting Aftab Ahmad Khan Sherpao, former Pakistani interior minister, local police told CNN.
The blast left blood-stained clothes, hats and shoes as well as body parts and pieces of flesh scattered across the mosque, according to reports.
The attack is the most recent in a series of attacks in Pakistan's North West Frontier Province and occurred near Sherpao's residence in Charsadda -- an area approximately 28 miles (45 kilometers) northeast of the city of Peshawar. Watch what's known about the blast »
Police investigators say Taliban or al Qaeda elements could have been involved and they believe the former minister was targeted over his supervision of operations against militants in Pakistan's tribal areas including the restive NWFP.
This attack is the deadliest in Pakistan since 136 people were killed in the southern port city of Karachi on October 18 in a suicide bombing targeting the convoy of Benazir Bhutto, Pakistan's former prime minister. See photos from the blast's aftermath »
Bhutto returned to the country after eight years in self-imposed exile ahead of January parliamentary elections.
The attack comes in the midst of continued operations by the Pakistani army to rout out militants in the swat valley in the north of the country, an area the government considers a front-line in the so-called global war on terror.
A former tourist destination about 100 miles (160 kilometers) from Islamabad, The Swat Valley has been plagued by violence and has become a hotbed for militants. Earlier this month, the army said it has retaken towns seized by militants over the summer, killing 290 and capturing 140.
The attack also comes less than a week after President Pervez Musharraf lifted a six-week-old state of emergency he said was necessary to ensure the country's stability but that critics said was a move to stifle the country's judiciary, curb the media and secure more power.
While Musharraf has promised free and fair parliamentary elections, continued instability in the tribal areas and the threat of attack on large crowds has kept people from attending political rallies and dampened the country's political process. Campaigners from various political parties say fewer people are coming out to show their support.
The president -- who survived two assassination attempts in December 2003 -- denounced Friday's attack, speaking out against what he said was a small number of Muslim extremists who would carry out such an act, according to a report from the state-run Associated Press of Pakistan. He ordered security and intelligence agencies to find those responsible.
A spokesperson for the U.N. said Secretary-General Ban Ki-moon condemns the attack and he "urges all political forces in Pakistan to unite against the scourge of terrorism and to act together to create a peaceful environment ahead of the Parliamentary elections."
This is the second attempt on Sherpao's life since April, when a suicide bomber blew himself up just a few feet from Sherpao during a political rally, injuring him and killing at least 28 people.
The APP reported that the blast was caused by a suicide bomber inside the mosque, as people were gathering for religious observances of Eid al-Adha, the Muslim celebration of the Hajj pilgrimage to Mecca in Saudi Arabia.
"We were saying prayers when this huge explosion occurred," said Shaukat Ali, a 26-year-old survivor of the blast whose white cloak and pants were torn and spattered with blood, an AP report said.
Despite security measures at the mosque, the bomber was praying in a row of worshippers when he detonated the explosive, provincial police chief Sharif Virk said, the report added.
A Peshawar hospital was wracked with chaos as the injured arrived in pickup trucks, ambulance sirens wailed and the wounded screamed for help, the report said. The bomb contained between 13-17 pounds of explosives and was filled with nails and ball bearings to maximize casualties, said the head of the bomb unit at the scene, who declined to give his name.
Sherpao and his two sons were in the first row of the mosque, the APP report said. Mustafa Khan Sherpao had leg injuries while Sikandar Hayat Khan Sherpao "escaped unhurt."
Sherpao was Pakistan's interior minister -- the country's top civilian security official -- before Musharraf announced a caretaker government in November ahead of elections. He heads the breakaway political group Pakistan People's Party-Sherpao, is a vocal critic of religious extremism, pro-Musharraf and a candidate in upcoming elections. E-mail to a friend
CNN's Mohsin Naqvi contributed to this report.