Any decision by South Korea to supply arms to Ukraine would make Seoul a participant in the conflict, the Kremlin said on Wednesday, after President Yoon Suk Yeol opened the door to such deliveries.

South Korea has denounced Russia's invasion of Ukraine and supplied economic and humanitarian aid to Kyiv, but unlike the United States and European allies has so far stopped short of sending weapons.

In a Reuters interview on Tuesday ahead of a visit to Washington next week, Yoon said Seoul would consider arming Kyiv in the event of a major new attack against Ukrainian civilians.

"Unfortunately, Seoul has taken a rather unfriendly position in this whole story," Kremlin spokesman Dmitry Peskov told reporters in a briefing.

"They will try to draw more and more countries directly into this conflict. But of course, the start of arms deliveries will obliquely mean a certain stage of involvement in this conflict."

Former Russian president Dmitry Medvedev, a close ally of President Vladimir Putin who frequently makes hawkish comments on Russia's military campaign in Ukraine, suggested Moscow could respond by supplying advanced weaponry to North Korea.

"I wonder what the inhabitants of this country [South Korea] will say when they see the latest designs of Russian weapons in the hands of their closest neighbors - our partners from the DPRK [North Korea]?" Medvedev said in a post on Telegram.