As many as 10,000 North Korean troops are in Russia's western front-line Kursk region and could engage in combat in the "coming days," a State Department spokesperson said Monday, amid growing concerns that their involvement could expand Moscow's war in Ukraine.

Matthew Miller, the spokesperson, made the remarks as Ukrainian President Volodymyr Zelenskyy said in a video message earlier that there are already 11,000 North Korean troops in the Kursk region.

"We now assess that as many as 10,000 have made their way to Kursk and could enter combat in the coming days," Miller told a press briefing.

Asked if North Korean soldiers are already in combat, Miller said he cannot speak to it definitely.

"But as we have said, we expected that it was likely that they would enter into combat against Ukrainian forces," he said. "And if they did, they would be legitimate military targets."

In a separate press briefing, Pentagon press secretary Maj. Gen. Pat Ryder said that the total number of North Korean service members in Russia could be between 11,000 to 12,000, including about 10,000 currently in the Kursk region.

He also noted that the total number of North Korean personnel in Russia could "go up slightly."

Regarding reports of North Korean troops already in combat operations, Ryder said that the Pentagon is looking into those reports.

According to a transcript posted on the Ukrainian president's official website, Zelenskyy gave an intelligence analysis showing that 11,000 North Korean troops are in the Kursk region.

"We are seeing an increase in North Koreans but, unfortunately, not an increase in our partners' response," the president said, calling for greater support from the international community. (Yonhap)