Ukrainian President Volodymyr Zelenskyy says it was absurd Russia had assumed the rotating presidency of the United Nations Security Council, adding this showed the institution's "total bankruptcy".
On Saturday Russia took over the presidency of the UN's top security body, which rotates every month.
The last time Moscow held the post was in February 2022, when its troops launched a full-scale invasion of Ukraine.
"Unfortunately, we ... have some obviously absurd and destructive news," Zelenskyy said in an evening video address, adding that Russian shelling had killed a five-month-old boy on Friday.
"And at the same time Russia is chairing the UN Security Council. It's hard to imagine anything that proves more the total bankruptcy of such institutions," he said.
The Kremlin said on Friday it planned to "exercise all its rights" in the role.
The United States on Thursday urged Russia to "conduct itself professionally" when it assumes the role, saying there was no means to block Moscow from the post.
Zelenskyy said it was time for a general overhaul of global institutions, including the Security Council.
"Reform is obviously necessary to prevent a terrorist state - and any other state that wants to be a terrorist - from destroying the peace," he said.
Earlier, Zelenskyy advisor Andriy Yermak also hit out at Iran, which Kyiv and its allies accuse of supplying Russia with arms. Tehran denies it is giving weapons to Russia.
"It is very telling that on the holiday of one terror state – Iran - another terror state – Russia – begins to preside over the UN Security Council," Yermak wrote on Twitter, referring to Iran's Islamic Republic Day holiday.
It is very telling that on the holiday of one terror state – Iran, another terror state – Russia – begins to preside over the UN Security Council.— Andriy Yermak (@AndriyYermak) April 1, 2023
It's not just a shame. It is another symbolic blow to the rules-based system of international relations.