It comes after the first official acknowledgement by Pyongyang and Moscow of North Korean troops' involvement in the Ukraine war.

South Korea's spy agency says an estimated 4,700 North Korean soldiers have been killed or wounded while fighting alongside Russia against Ukrainian forces.

North Korea earlier this week conducted the first test-firing of the weapons system of the new "Choe Hyon-class" warship it recently unveiled, state media KCNA reported on Wednesday.Cruise and anti-air missiles were launched and artillery fired as part of the test-firing attended by leader Kim Jong Un and senior officials,