The South Korean military says it believes more than ten-thousand North Korean troops have been deployed to Russia in support of the military offensive in Ukraine.

At a press briefing Tuesday, defense ministry spokesperson Jeon Ha-kyu said intelligence authorities in South Korea and the U.S. believe a “considerable number” have been sent to the front lines, including Russia’s Kursk border region.

While military intelligence agencies in the South are monitoring the situation, the spokesperson declined to verify a local media report that some 40 North Korean soldiers were killed in action.

On Monday, U.S. State Department spokesperson Matthew Miller said as many as ten-thousand North Korean troops have made their way to the Kursk region and could enter combat “in the coming days.”