Biden says Russia 'shamelessly violated' U.N. principles in its invasion of Ukraine after Putin escalates conflict

WASHINGTON — President Joe Biden slammed Russia’s invasion of Ukraine as having “shamelessly violated” United Nations principles during a speech to the world body Wednesday, hours after Russian President Vladimir Putin appeared to threaten to use nuclear weapons against Kyiv.

“Russia has shamelessly violated the core tenets of the U.N. charter — no more important than the clear prohibition against countries taking the territory of their neighbors by force,” Biden told the U.N. General Assembly. “If nations can pursue their imperial ambitions without consequences, then we put at risk everything this very institution stands for.”

In a roughly 30-minute speech, he said that the war in Ukraine was about “extinguishing Ukraine’s right to exist as a state … and Ukraine’s right to exist as a people,” calling out Putin for making “irresponsible nuclear threats.”

“A nuclear war can never be won and must never be fought,” Biden said in his speech.

His remarks to nearly 200 world leaders gathered for the first in-person U.N. General Assembly since the pandemic hit came just hours after Putin delivered an address announcing the partial mobilization of military reservists, a significant escalation of his war in Ukraine. In the same speech, Putin appeared to threaten nuclear retaliation if Kyiv continues its efforts to reclaim occupied territory.

The gathering comes at a perilous time on a number of fronts. Russia’s war in Ukraine has upended global food supplies and threatens to tip Europe into a recession this winter as the continent braces for a surge in energy costs. The United States is also facing heightened tensions with China, which has shown signs of increasing aggression toward Taiwan. And climate change continues to be one of the most daunting international challenges.

In his speech, Biden announced $2.9 billion in new U.S. government assistance to combat "acute food insecurity" that he said was caused by the war in Ukraine and climate change.

He again warned of a global “contest between democracy and autocracy” — a major theme of his presidency that he has sought to champion on the world stage even as he has raised alarms about the internal threats to America’s own democratic values.

Biden, who has repeatedly accused former President Donald Trump and his supporters of promoting an extreme ideology that threatens democracy, said Wednesday that the U.S. was “determined to defend and strengthen democracy at home and around the world.”

“I believe democracy remains humanity’s greatest instrument to address the challenges of our time,” he said.

At a fundraiser in New York on Tuesday night, Biden warned donors about the “MAGA crowd” and said the U.S. was at “an inflection point.” “You can’t claim to be a democrat with a small d if you engage in violence against the government,” he told the crowd.

Biden comes into the meeting on firmer ground than last year when his speech came just weeks after the deadly and chaotic U.S. withdrawal from Afghanistan had global leaders questioning America's leadership role in the world.

Now, U.S. efforts to support Ukraine in its fight against Russia have shown significant signs of progress in recent days after Kyiv reclaimed territory in the northeastern Kharkiv province, in what many observers said could be a decisive shift as the war nears its seventh month.

Ukrainian President Volodymyr Zelenskyy will address the group virtually later Wednesday. Putin said last month he would not attend the meeting.

On China, Biden faces a delicate balancing act as tensions have escalated in recent months. During an interview on CBS' "60 Minutes" that aired Sunday, he said that U.S. forces would defend Taiwan if China invaded, a position criticized by Beijing.

It is at least the fourth time since last year that Biden has made comments that appear to alter long-standing U.S. policy on Taiwan, though White House officials have said there has been no change in the policy.

"We seek to uphold peace and stability across the Taiwan Straits and remain committed to our one-China policy, which has helped prevent conflict for four decades," Biden said Wednesday.

The U.S. is bound by law to provide Taiwan with defensive weapons, but it has a policy of “strategic ambiguity” when it comes to exactly how it would respond to Chinese aggression toward the island.

Chinese President Xi Jinping did not attend the U.N. meeting.

Biden arrived in New York on Tuesday, a day after returning to Washington, D.C., from London where he joined other world leaders in attending Queen Elizabeth II's funeral.

While in New York, he also met Wednesday with U.N. Secretary-General António Guterres and new British Prime Minister Liz Truss. He will also speak at the Global Fund conference on the fight against AIDS, tuberculosis and malaria, and host a reception with other world leaders at the American Museum of Natural History.

This article was originally published on NBCNews.com