Ukrainian President Volodymyr Zelenskyy says there are already 11,000 North Korean troops in the Kursk region of western Russia, on the border with his country.

In a video address to the nation on Monday, Zelenskyy said intelligence reports suggested increasing North Korean troops there, but said: “Unfortunately, not an increase in the response of our partners.”

Last Friday, he said that Ukraine can see all the places where North Koreans gather on Russian territory. He called on Western countries to allow Ukraine to use long-range weapons against targets in Russia.

U.S. State Department spokesman Matthew Miller said the department estimates that up to 10,000 North Korean troops have headed to Kursk. He added that they could enter combat in the coming days.

Ukrainian Defense Minister Rustem Umerov told a South Korean broadcaster that Ukrainian and North Korean troops had clashed for the first time.

Referring to the reports, US Department of Defense spokesperson Pat Ryder said: “We are investigating them, but at this time we cannot corroborate those reports.”

He added that if North Korean troops participate in combat support operations against Ukraine, they would become legitimate military targets.