US, Japanese and South Korean security advisers have expressed grave concern about the dispatch of North Korean troops to Russia for possible use on the battlefield against Ukraine.

John Kirby, the White House national security spokesperson, told reporters on Friday that US National Security Advisor Jake Sullivan and his Japanese and South Korean counterparts, Akiba Takeo and Shin Won-sik, held talks in Washington.

Kirby said the three officials agreed that the deployment is the latest in a series of concerning indicators of deepening military cooperation between North Korea and Russia. He added that the officials called on the two countries to cease these actions.

Kirby said there may be more than 3,000 North Korean soldiers in Russia.

He said their future role remains unknown, but he pointed out that at least some of them could be deployed to the Kursk region in Russia's west. He added Washington is closely watching the situation.