South Korea’s presidential office demanded an official explanation and apology from Ukraine for disclosing the transfer of two North Korean prisoners of war to South Korea, according to the Hindustan Times, in a text from the Reuters feed.

Seoul says Ukraine repeatedly asked for secrecy through various channels about the operation. The presidential office said Ukraine’s denial that any confidentiality agreement existed was false and had damaged trust between the two governments, according to Nikkei Asia, citing Reuters.