PESHAWAR - The leader of the Pakistani Taliban, the militant movement that poses the gravest security threat to the country, was believed killed by a US drone strike, four Pakistan intelligence officials told Reuters on Sunday.The officials said they intercepted wireless radio chatter between Taliban fighters detailing how Hakimullah Mehsud was killed while traveling in a convoy to a meeting in the North Waziristan tribal region near the Afghan border.A senior military official told Reuters there was no official confirmation that the Pakistani state's deadliest enemy had been killed. The Pakistani Taliban issued a denial.