South Korea has demanded a full explanation and apology from Ukraine, accusing it of disclosing the transfer of two North Korean prisoners of war to the country without its consent.

Seoul also accused Kyiv of falsely denying that the two countries had agreed to keep the transfers of North Koreans caught fighting for Russia secret.

The diplomatic spat comes after Ukrainian President Volodymyr Zelenskyy told the UN General Assembly last week that his country had transferred two North Korean soldiers to South Korea after they were caught fighting for Russia.

Seong Ghi-hong, senior presidential secretary for public relations, said in a statement on Sunday that the government was reviewing additional measures over the issue if necessary.

Mr Seong said Ukraine had repeatedly discussed the prisoners' transfer with Seoul through various channels and had requested secrecy, arguing that public disclosure could trigger domestic criticism that Kyiv had given up an opportunity to exchange the soldiers for Ukrainian prisoners.

He said South Korea agreed to keep the transfer confidential given security, diplomatic and humanitarian concerns, including the safety of the prisoners and their families.

Last week's disclosure at the UN General Assembly was done without sufficient prior consultation and Ukraine subsequently denied the existence of any confidentiality agreement, he added.

The issue had seriously damaged trust between Seoul and Kyiv, he said, adding it could harm bilateral relations.

Ukraine's embassy in Seoul did not respond to a request for comment from Reuters.

Alexander Hynd, a lecturer at the University of Melbourne's Asia Institute, told the ABC the incident had damaged relations between the two countries and an apology was unlikely to change that.

"For South Korean President Lee, accepting the North Korean prisoners of war is not a diplomatic coup to be publicised at the UN, but rather complicates his attempts at better relations with North Korea," Dr Hynd said.

"Prior to this incident, South Korean leaders were already cautious about proposals that Seoul should share air defence systems and other military equipment [with Ukraine].

"In my view this incident makes it even less likely that the Lee administration agrees to future arms transfers." Announcement 'deeply regrettable'

South Korean President Lee Jae Myung days earlier said Ukraine had disclosed the transfer in breach of a non-disclosure agreement.

In a post on X, Mr Lee said both countries had agreed to keep the transfer confidential.

"I do not know what circumstances led the Ukrainian side to disclose the matter despite the confidentiality agreement, but it is deeply regrettable," he wrote.

"The issue of bringing North Korean prisoners to South Korea is a highly sensitive one that could have a major impact on diplomacy, security and the situation on the Korean Peninsula."

Last week, Ukrainian presidential aide Dmytro Lytvyn said Ukraine was "an open country" and it would have been strange to hand them over in secret.

"From the entire story, which is long and detailed, we reported only the fact itself, that they were sent to the Republic of Korea," he said.

Ukraine captured the two North Koreans in Russia's Kursk region in January 2025, the first soldiers from the country to be captured alive since Pyongyang sent troops to help Russia in 2024.

South Korea had previously declined to confirm the soldiers' arrival, citing concerns for their safety and that of family members still in North Korea.

Seoul and Kyiv had been discussing a possible transfer after the two soldiers expressed a desire to go to South Korea, according to an opposition MP in Seoul.

The transfer comes as South Korea has backed efforts to revive dialogue with North Korea, while US President Donald Trump has renewed his willingness to engage with Pyongyang.