North Korea has deployed thousands of troops to support Russian forces fighting in Ukraine, according to Ukrainian, U.S. and South Korean assessments, Pyongyang's first major involvement in a war since the 1950s.

China, Russia and North Korea have formed a “triangle of troublemakers” that threatens to transform the Pacific region, a senior US commander has warned, even as President Donald Trump seeks warmer ties with two of those adversaries.

The deployment of thousands of North Korean troops marks the country's first participation in a large-scale conflict since the end of the Korean War.