South Korea's President Lee Jae Myung has threatened unspecified "further action" if Ukraine does not issue a public apology over the disclosure that two North Korean prisoners of war had been transferred to the South.
Ukrainian President Volodymyr Zelensky made the revelation at the UN General Assembly last week, drawing sharp condemnation from Seoul, which said the move was meant to remain confidential.
Ukraine's Foreign Minister Andrii Sybiha described the situation on Thursday as a "diplomatic misunderstanding" and said Kyiv was "working" to resolve it.
Lee rejected that characterisation, writing on X that the matter concerned "the dignity of the Korean people and the nation."
Lee's office said it was Ukraine that had requested the transfer be kept secret, partly to protect the North Korean soldiers' families and partly because Kyiv wanted to avoid criticism that it had passed up an opportunity to exchange the men for Ukrainian prisoners of war.
Zelensky's office disputed this, saying the two countries had no such confidentiality agreement, further escalating the dispute.
Lee himself came under heavy domestic criticism following Zelensky's disclosure, with the South Korean opposition accusing him of concealing the transfer in order to appease Pyongyang.
The two soldiers were among thousands of North Koreans reported to be supporting Russia in the war in Ukraine. They had previously told local media they wished to be sent to South Korea.
Speaking to Ukrainian media on Thursday, Sybiha said he "hopes that this situation will be resolved in the very near future."
"We are working on it. For us, South Korea is an important country. And I really hope for momentum, continuation, and concrete results that we are truly achieving with them," he said.
Lee responded by accusing Kyiv of attempting to "bring war on the Korean Peninsula."
"We express serious regret that, instead of acknowledging the facts of the agreement and apologising, they are talking about an imminent military clash between the North and South," he wrote on X.
South Korea has expressed sympathy for Ukraine since Russia's full-scale invasion but has maintained its longstanding policy of not supplying lethal weapons to any country engaged in active conflict.
