South Korea's President Lee Jae Myung has threatened to take unspecified "further action" if Ukraine does not issue a public apology for revealing that two North Korean prisoners of war had been sent to the South.

Ukraine's leader Volodymyr Zelensky made the disclosure to the UN general assembly last week, angering Seoul, who said the move was meant to stay secret.

Ukraine's Foreign Minister Andrii Sybiha on Thursday described the situation as a "diplomatic misunderstanding", adding that Kyiv was "working" to resolve it.

Lee rejected this characterisation on X, saying it concerned "the dignity of the Korean people and the nation".

Lee's office said last week that it was Ukraine that requested for the move to be kept secret, partly to protect the North Koreans' families, and also because Kyiv wanted to avoid criticism that it had given up an opportunity to exchange the soldiers for Ukrainian prisoners of war.

Zelensky's office responded, saying the two countries had no such agreement to keep the move confidential, further escalating the situation.

Lee himself faced heavy criticism at home after Zelensky's disclosure, with the South Korean opposition accusing him of covering up the transfer to appease Pyongyang.

The two soldiers, who were among thousands of North Koreans supporting Russia in the Ukraine war, had earlier told local media they wanted to be sent to South Korea.

Speaking to Ukrainian media on Thursday, Sybiha, the foreign minister, 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, in response, accused 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 said in an X post.

Seoul has been sympathetic to Ukraine since Russia's full-scale invasion, but has adhered to its longstanding policy of not providing lethal weapons to any country engaged in active war.