Zelenskyy criticized Guterres in an evening speech on Thursday that marked United Nations Day, in which he said it is “crucial” the world remembers the goals and principles of the U.N. Charter.

“Even if some officials prefer the allure of Kazan over the substance of the U.N. Charter, our world is structured so that the rights of nations and international legal norms matter, and will continue to matter,” said Zelenskyy in his address.

Ukraine’s Foreign Ministry earlier also slammed the U.N. chief for his attendance decisions.

“The UN Secretary General declined Ukraine’s invitation to the first global peace summit in Switzerland. He did, however, accept the invitation to Kazan from war criminal Putin,” Ukraine’s Foreign Ministry posted on X on Monday. “This is a wrong choice that does not advance the cause of peace. It only damages the UN’s reputation,” the post continued.

Not only Ukraine criticized Guterres over his visit.

Guterres’ move garnered various reactions, including from Lithuanian Foreign Minister Gabrielius Landsbergis, who indirectly challenged the U.N. head to step down.