The UN General Assembly (UNGA) overwhelmingly approved a resolution on Wednesday telling Russia its annexation of four Ukrainian zones is illegal and not valid.
Ukrainian President Volodymyr Zelensky called the resolution "historic" in a tweet and thanked the states that voted in favor.
During the assembly's emergency special session on Ukraine, US ambassador to the UN Linda Thomas-Greenfield said the vote "is important not just to the future of Ukraine and the future of Europe, but to the very foundations of this institution."
"After all, the UN was built on an idea: that never again would one country be allowed to take another's territory by force," Thomas-Greenfield added.
The US diplomat said the resolution calls for peace and de-escalation, and "makes clear that we reject Russia's attempted annexations. That we reject this affront to territorial integrity, to national sovereignty, to peace and security."
She noted that "today it is Russia invading Ukraine. But tomorrow it could be another nation whose territory is violated. You could be next. What would you expect from this chamber?"
"So let us send a clear message today: these United Nations will not tolerate attempts at illegal annexation. We will never recognize it. These United Nations will not tolerate seizing a neighbor's land by force. We will stand up to it. These United Nations will not tolerate the destruction of the UN Charter. We will defend it," she told the assembly.
"Our message Today is loud and clear: It does not matter if you, as a nation, are big or small, rich or poor, old or new. If you are a UN Member State, your borders are your own and are protected by international law. They cannot be redrawn by anyone else by force." Thomas-Greenfield added.