South Korea said Tuesday it will withdraw some staff from its embassy in Kyiv, deepening a diplomatic row over Ukraine’s announcement last month of a transfer of two North Korean prisoners of war that Seoul says was meant to be secret.

Axar.az reports, citing AP, the diplomatic dispute between the countries began after Ukrainian President Volodymyr Zelenskyy disclosed the prisoners’ transfer during a Sept. 23 speech at the United Nations. South Korea has accused Ukraine of violating a nondisclosure agreement, but Ukraine denies the countries reached such a deal, further angering Seoul.

South Korea recalled its ambassador to Ukraine earlier this month in protest. Ukrainian Foreign Ministry spokesperson Heorhii Tykhyi told local media at the time that Kyiv remains open to “constructive dialogue” and that “diplomacy must prevail over emotions.”

South Korean Foreign Ministry spokesperson Park Doosoon said Tuesday that the withdrawal of additional embassy staff was due to Ukraine’s “lack of constructive steps” to address Seoul’s grievances as well as concerns about safety amid intensifying Russian attacks.

Park did not specify how many staff members would withdraw or when. He said South Korea would keep its charge d’affaires and essential personnel in Kyiv to maintain contact with Ukrainian authorities and assist South Korean citizens.