South Korea and the United States, which are conducting their own annual military drills until the end of April, are watching the North Korea’s activities for signs it will go from exercise to an actual attack, a South Korean official said.

“It hasn’t been frequent that the North conducted military exercise at the state level,” South Korea’s defence ministry spokesman Kim Min-seok said. “The North is currently conducting various drills on land, at sea and aerially.”

“We are watching the North’s activities and stepping up readiness under the assumption that these drills can lead to provocation at any time.”

Mr Kim declined to confirm news reports that the North has imposed no-fly zones off its coasts in a possible move to fire missiles, but he said any flight ban limited to near the coast would not be for weapons with meaningful ranges.