The dispute erupted after Ukrainian President Volodymyr Zelenskyy announced at the United Nations General Assembly that Kyiv had handed over two North Korean soldiers, seized while fighting alongside Russian forces, to South Korea.
Seoul claims an agreed‑upon confidentiality clause was violated, arguing the transfer should remain undisclosed to protect the POWs' safety.
Lee Jae Myung posted on X on Friday that unless Kyiv admits the breach and issues a public apology, Seoul will take "additional measures"—though he did not specify which.
He also voiced "grave regret" over Ukrainian remarks suggesting a potential clash between North and South Korea, labeling them as encouragement of war on the peninsula.
Ukrainian Foreign Minister Andrii Sybiha counters the accusation, calling the incident a "diplomatic misunderstanding" and indicating Kyiv seeks to mend ties with Seoul.
The situation arrives at a crucial juncture for Lee's administration, which is already wrestling with domestic backlash over a recent landmine incident in the DMZ and hopes to maintain a thaw with Pyongyang.
The next step may involve a formal diplomatic protest from Seoul and potential sanctions, or a meeting between Seoul and Kyiv officials scheduled for early next month.