Russian President Vladimir Putin has not denied claims that North Korean troops are in Russia, with Ukraine’s intelligence agency saying Thursday that the soldiers had already arrived in Russia’s Kursk region.

Asked by a reporter Thursday about satellite imagery showing apparent North Korean troop movements, Putin gave a seemingly tongue-in-cheek response: “Images are a serious thing. If there are images, it means they reflect something.”

The comments were his first on U.S., Ukrainian and South Korean assessments that Pyongyang had dispatched soldiers to join Moscow’s war effort against Ukraine.