A powerful explosion has killed at least two people in Pakistan ' s troubled northwestern tribal region, security sources say.A bomb exploded near a mosque in Kohat, a main city of Khyber Pakhtunkhwa province on Thursday. The explosion happened just as worshipers were leaving the mosque after noon prayers. Local security officials said the bomb was planted in a motorcycle parked near the mosque and the explosion was carried out through a remote - controlled device. “Between four and five kilograms of explosive material was used in the bomb. I can confirm the death of two people and seven people were injured, ” the dailyDawn newspaper quoted Kohat District Police officer Dilawar Bangash as saying. Security officials said they have cordoned off the area after the blast, and launched an investigation into the incident. No group or person has yet claimed responsibility for the deadly attack, but pr-Taliban militant groups have been blamed for such attacks in the past. Pakistani security forces have launched several operations in the troubled northwest in a bid to flush out militants from its tribal zone. Despite the Pakistani government's operations against Tehrik-e Taliban Pakistan (TTP) militants and associated groups, they have been able to spread their influence in various regions of the country and kill thousands of people. Thousands of Pakistanis have lost their lives in bombings and other militant attacks since 2001 when Pakistan entered an alliance with the US in its so-called war against terrorism. Thousands of Pakistanis have lost their lives in bombings and other militant attacks since 2001, when Pakistan entered an alliance with the US in the so-called war on terror. Thousands more have been displaced by the wave of violence and militancy sweeping across the country.