It followed an impressive parade Saturday to mark the "Day of the Sun," the most important day in the North Korean calendar, when Pyongyang showed off an array of new missiles and launchers.

Tensions on the Korean Peninsula have ratcheted up in recent weeks, amid tit-for-tat saber-rattling from the US and North Korea.

On Sunday, US National Security Adviser H. R. McMaster said the problem with North Korea "is coming to a head. And so it's time for us to undertake all actions we can, short of a military option, to try to resolve this peacefully."

Last month during a visit to South Korea, US Secretary of State Rex Tillerson said Washington's policy of "strategic patience" with Pyongyang had ended.