SEOUL — South Korea’s president threatened Friday to take unspecified punitive steps against Ukraine if it refuses to apologize over its revelation of a supposedly secret transfer of two North Korean prisoners of war to South Korea. Seoul and Kyiv are embroiled in a diplomatic dispute, with Seoul strongly protesting against Ukrainian President Volodymyr Zelenskyy’s disclosure of the transfer during his U.N. speech last week. South Korea accuses Ukraine of violating a nondisclosure agreement on the transfer, but Kyiv has denied agreeing to such a deal. The arrival of the North Korean soldiers in mid-September could also spell trouble for South Korea's liberal government, which hopes to improve ties with Pyongyang. But despite an escalation in its rhetoric, many experts say Seoul isn't likely to take any drastic steps because maintaining good relations with Ukraine is in its national interests and will support its partnerships with other Western nations. The soldiers had been among thousands of North Korean troops sent to support Russian President Vladimir Putin’s war against Ukra