"The scale of deployed North Korean troops is being closely watched," Yoon Yeocheol, South Korea's ambassador to the U.K., told Newsweek.

Ukrainian and South Korean intelligence services have said that many of the troops deployed to Russia are some of Pyongyang’s best, drawn from the 11th Corps, also known as the Storm Corps - a unit trained in infiltration, infrastructure sabotage and assassinations.

North Korea could send as many as 100,000 troops to support Russia's war in Ukraine, according to reports from assessments by some G20 nations, sparking fears of a dramatic escalation in the conflict.