NEW: South Korean President Lee Jae-myung has threatened "further action" unless Ukraine publicly apologizes for revealing that two North Korean prisoners of war were transferred to South Korea.

NEW: South Korean President Lee Jae-myung has threatened "further action" unless Ukraine publicly apologizes for revealing that two North Korean prisoners of war were transferred to South Korea.

Zelensky revealed the transfer at the UN General Assembly, angering Seoul, which it says was supposed to remain secret in part to protect the soldiers' families. Kiev denies there was any non-disclosure agreement.

Ukraine called the dispute a "diplomatic misunderstanding," but Lee rejected that explanation, accusing Kiev of trying to "bring war on the Korean peninsula."