Ukrainian President Volodymyr Zelenskyy says there are already 11,000 North Korean troops in the western Russian region of Kursk bordering his country.

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

Last Friday, he said Ukraine can see every site where North Koreans are assembling on Russian territory. He called on Western countries to allow Ukraine to use long-range weapons against targets in Russia.

US State Department Spokesperson Matthew Miller said the department assesses that as many as 10,000 North Korean troops have made their way to Kursk. He added that they could enter combat in the coming days.

Ukraine's Defence Minister Rustem Umerov told a South Korean broadcaster that Ukrainian and North Korean troops had confronted each other for the first time.

Referring to the reports, the US Defense Department spokesperson Pat Ryder said, "We are looking into those, but at this point cannot corroborate those reports."

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