North Korea said the withdrawal of its invitation to a US envoy was a response to provocative manoeuvres by US B-52H bombers, dpa quoted local news reports as saying Sunday. "US and South Korean joint military excercises over the Korean Peninsula are a military threat," Pyongyang's Foreign Ministry said in a statement quoted by the North's state-run Korean Central News Agency. US and South Korean forces ended a 12-day series of joint military excercises on Friday, including a computer-simulated conflict, but it was not clear whether the bombers were deployed during the drill. The special envoy, Robert King, was to travel at the invitation of Pyongyang on a humanitarian mission focused on securing the release US citizen Kenneth Bae, the State Department announced Friday. The invitation was withdrawn the same day, the department said later, adding "We are surprised and disappointed by North Korea's decision."