At least one person has been killed and 30 wounded in a blast at the offices of a pro-Taleban group in north-west Pakistan, local officials say.
The explosion appeared to target a religious organisation called the Promotion of Virtue and Prevention of Vice in the Khyber tribal region.
A group spokesman said the blast was the work of a suicide attacker.
Some observers say the group has a history of militancy and explosives may have detonated by accident.
'Blew himself up'
A spokesman for the group, Munsif Ali Khan, told the BBC it was a suicide attack, carried out by a teenage man, just after the daily teachings from the Koran when the group's head, Haji Namdar asked for donations.
"The boy was about 18 or 19," Munsif Khan said. "He got up and walked towards [Haji Namdar] with a pistol in his hand which he wanted to donate. He blew himself up just when he was handing the gun to the amir."
The spokesman said the attacker and Haji Namdar were holding hands at the time. He said the young man died, but that Haji Namdar was not harmed at all.
"This is the third time God has saved [Haji Namdar]. Twice before he was targeted by bomb attacks, but every time he remained unharmed."
Some of the injured are said to be in a critical condition.
An official of the Khyber administration told the BBC that the Promotion of Virtue and Prevention of Vice group was suspected of involvement in the kidnapping of World Food Programme officials as well as the kidnapping of more than 10 Pakistani paramilitary personnel in the Khyber region earlier this year.
The hostages were subsequently released.
The organisation denies the charges and says it intervened to get the hostages freed.
The Khyber official also said the organisation was suspected of carrying out suicide attacks in Afghanistan's eastern Nangarhar province.
Khyber is one of seven semi-autonomous tribal regions along the Afghan border.
Last month, a suicide bomber in a car attacked a Pakistani army base near the Afghan border, killing five troops and injuring nine.