KHYBER, Pakistan - A blast ripped through a congregation of worshippers during Friday prayers at a mosque in Pakistan's northwestern tribal region of Khyber, killing at least 26 people, government officials said. More than 60 people were also wounded in the attack in Jamrud, the main town of Khyber, where militants have been active for the past several years. "According to initial reports about 20 people have been killed in the blast but the toll could rise as many wounded are in serious condition," government official Khalid Mumtaz Kundi said. Another official put the death toll at 26. Local media said the blast was a suicide bombing carried out by a teenager. There were still bodies trapped in the wreckage, said a witness, Haji Zarmeen, who helped removed at least 12 bodies from the rubble. No one has claimed responsibility for the attack. Pakistan has seen a wave of violence in recent years in which thousands of people have been killed. There have been several bomb attacks since US special forces killed al Qaeda chief Osama bin Laden in a secret raid in a Pakistani town in May. Al Qaeda-linked militants have vowed to avenge bin Laden's death.