At least six people were killed and several others in a dual blast on Sunday morning in Pakistan's Dera Ismail Khan district.In the first attack, two police were killed and several others injured when some unknown militants sprayed bullets at a police check post and fled the scene, reported Xinhua news agency.The second attack happened at a hospital where the policemen were shifting their injured colleagues, Deputy Superintendent of Police Iftikhar Shah said.A female suicide bomber blew herself up near the policemen at the main gate of the hospital, leaving four more policemen killed and scores other injured, he added.No group or individual has claimed the attack.Dera Ismail Khan is a main district in the country's northwest Khyber Pakhtunkhwa province, which used to be a hotbed of militancy, but terrorism has been curtailed greatly after years of military operation in tribal areas to remove sanctuaries of terrorists.Analysts believe that the backbone of the militants has been broken, but they still have some resources left to carry out sporadic attacks on security forces and general public.