Heavily armed militants thought to have been trying to free associates when they stormed Dera Ismail Khan jailTaliban militants disguised as police and armed with guns, rocket-propelled grenades and explosives attacked a prison in north-west Pakistan holding 40 "high-profile" inmates Monday night in an apparent attempt to free associates, officials said.Pakistani Taliban spokesman Shahidullah Shahid claimed responsibility for the attack, saying 150 militants took part and around 300 prisoners were freed.The attack in the town of Dera Ismail Khan began around midnight with a huge explosion, said intelligence officials.