Pakistani troops have ended a siege by militants who attacked a naval base in the city of Karachi, navy sources say.The troops are now said to be “mopping up” after the raid, which has left at least 12 soldiers dead.The attackers were said to have been holed up in an office building with hostages after storming the Mehran naval aviation base overnight.The Pakistan Taliban says the raid was to avenge Osama Bin Laden’s killing by US special forces on 2 May.”It was the revenge of martyrdom of Osama Bin Laden. It was the proof that we are still united and powerful,” Ehsanullah Ehsan told Reuters news agency.They have carried out several attacks since then.