At least 21 people were killed and 78 injured on Friday after a bomb exploded inside a mosque in northwestern Pakistan. 15 police officers were among those killed as the attack happened near a building housing police offices. The attacker rammed an explosives-laden vehicle into the mosque in Kohat, a district in Khyber Pakhtunkhwa province bordering Afghanistan, said the provincial police chief, Zulfiqar Hameed. The attack left the outer wall of the police offices collapsed and the mosque badly damaged. Two armed men attempted to enter the police premises and exchanged fire with officials there, police said. One of the attackers has been killed, the BBC reported.