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

On the one hand, the deployment of the North Korean troops seems a logical follow-up to the mutual defense treaty signed by Kim Jong-un and Vladimir Putin in Pyongyang in June. On the other hand, it raises a series of important questions.

SEOUL (Reuters) -North Korean leader Kim Jong Un urged the country's military to improve capabilities for fighting a war in a speech last week, state media KCNA said on Monday, after Pyongyang dispatched thousands of troops to Russia.