South Korea’s presidential office has demanded an apology from Ukraine for denying an agreement to keep the transfer of two North Korean prisoners of war to Seoul confidential.

The row was ignited by Ukrainian President Volodymyr Zelenskyy’s disclosure last week that his country had sent two North Korean soldiers to the South, adding they were “not easy to capture alive.”

The intensifying dispute risks complicating Kyiv’s efforts to obtain weapons from allies including South Korea to fight off bombardments from Russia.