At least 20 people, mostly security personnel, were killed and 14 others wounded in a suicide bomb blast in northwest Pakistan. Officials said, a suicide bomber rammed his explosives-laden vehicle into Miryan police station in Bannu district of Khyber-Pakhtunkhwa province on Wednesday evening. The explosion, which was heard several kilometers away, flattened the police station and a nearby mosque.Toll is expected to rise as some persons could be buried in the rubble of the police station and mosque. Security officials said most of the dead were policemen and Frontier Corps personnel. The blast also destroyed part of a girls' primary school.Bannu borders the volatile North Waziristan and South Waziristan tribal regions that are considered strongholds of the Pakistani Taliban.