North Korea's ambassador to the United Nations in Geneva on Tuesday defended his country's use of "tough counter-measures" against what he said was US aggression, hours after the nuclear-armed nation fired a ballistic missile over Japan.

"Now that the US has openly declared its hostile intention towards DPR Korea by raising joint aggressive military exercises despite repeated warnings... my country has every reason to respond with tough counter-measures as an exercise of its rights to self-defence", Han Tae-Song told the Conference on Disarmament, without directly referring to Tuesday's rocket launch.