South Korea says it has written documents proving that Seoul and Kyiv agreed to keep the transfer of two North Korean prisoners of war (POWs) secret, as President Lee Jae Myung warned Friday that Seoul will take "additional measures" if Ukraine refuses to apologize for disclosing the transfer. The remarks are expected to deepen diplomatic standoff between the two countries after Ukrainian President Volodymyr Zelenskyy announced the transfer during his U.N. General Assembly address on Sept. 23. Kyiv has denied any confidentiality agreement existed, while Seoul insists one was clearly in place and that Ukraine broke it. A senior foreign ministry official laid out Seoul's account of events in detail on Friday. "It is clear that the two countries agreed to keep the transfer secret," the official told reporters. "The Ukrainian side notified the South Korean side that Zelenskyy would make a speech at the U.N. General Assembly, without specifying its content. The South Korean side responded by text, saying it wanted Zelenskyy not to breach the agreement between the two nations on keeping the t