The explosion was reported in the basement of the Tableeghi Markaz seminary, near Mingora, regional headquarters of the scenic Swat district. The district was once a Taliban militant stronghold and came to international notice after the near fatal shooting of Malala Yousafzai, a brave 15-year-old education activist, by Taliban militants as she rode a school bus.
Pakistan's Dawn newspaper quoted a senior district official that the Thursday blast occurred when hundreds of people, arriving for Thursday night prayers, had assembled in the basement of the facility to be away from the cold.
The powerful blast shattered windows and doors of the center's hall, the report said. Both the dead and the injured were taken to the district hospital in Saidu Sharif.
A hospital doctor was quoted as saying many of the victims appeared to have been hit by explosives and bore shrapnel and ball-bearing marks.
One eyewitness told Dawn the explosion occurred as those praying stood up for ablution at the center.
Swat, known for its green valleys and snow-covered mountains, had remained under the control of militants until April 2009, when the Pakistani security forces launched a major operation to regain control of the area.
Local Taliban leader, Maulana Fazlullah, fled Swat during the operation.
Dawn quoted Pakistani officials that the Maulana and fighters are believed to be hiding in neighboring Afghanistan, from where they try to sneak into Swat.
The Swat attack came on the same day when separate explosions and suicide bombings in another part of Pakistan killed more than 90 people and injured about 170 people in Quetta, capital of Baluchistan province, which has been the scene of much sectarian and separatist violence. Many of those killed in the Quetta attacks were believed to be members of the Shiite Muslim minority in Sunni-majority Pakistan.