United Nations(CNN) President Joe Biden on Wednesday declared Russia's invasion of Ukraine a violation of the global order, sharpening his rebukes of President Vladimir Putin as the war entered a tense new moment.
Biden's speech at the United Nations General Assembly came hours after Putin announced an expansion of his war effort, lending the annual address Cold War-style gravity as Biden sought to rally nations behind his effort to isolate and punish Russia.
"This war is about extinguishing Ukraine's right to exist as a state and Ukrainians' right to exist as a people," Biden told the international body. "That should make your blood run cold."
Speaking inside the soaring General Assembly hall, Biden called the seven-month-old invasion a "brutal, needless war" that amounts to a "shameless violation" of the United Nations charter.
"Putin claims he had to act because Russia was threatened, but no one threatened Russia and no one other than Russia sought conflict," Biden said in his speech.
Biden returned to the green-marbled United Nations stage Wednesday hours after Russia's president delivered his provocative speech, setting up a rhetorical showdown between the two leaders on the international stage.
Putin's speech dramatically illustrated the challenges that lie ahead in Biden's efforts to sustain Ukraine and punish Moscow. The combined effects of the prolonged conflict and economic uncertainty have created a dark mood among world leaders gathering in New York this week for the annual high-level UN meetings.
Biden had already planned to make the Ukraine war a centerpiece of his yearly UN address, with aides previewing a harsh message for Moscow. But Putin's announcement that he was ordering a "partial mobilization" of Russian citizens in the Ukraine war and again raising the specter of using nuclear weapons dramatically increased the stakes for Biden's address.
Biden accused Putin of making "irresponsible nuclear threats" in his speech, and declared "a nuclear war cannot be won, and must never be fought."
"Let us speak plainly: A permanent member of the United Nations Security Council invaded its neighbor, attempted to erase the sovereign state from the map," he said.
Hours earlier, in his 20-minute speech, Putin warned he would use "all the means at our disposal" if he deemed the "territorial integrity" of Russia to be jeopardized. The mobilization means citizens who are in the reserve could be called up, and those with military experience would be subject to conscription, Putin said, adding that the necessary decree had already been signed and took effect on Wednesday.
In response, Biden said Putin was waging a war meant to demolish the Ukrainian nation.
"We will stand in solidarity against Russia's aggression, period," he said.
Biden warned that the basis of the United Nations' charter is "under attack" amid Russia's war in Ukraine, which he cast as a "shameless" violation of the body's founding document.
"As we meet today, the UN charter's very basis of a stable and just rule-based order is under attack by those who wish to tear it down or distort it for their own political advantage," Biden said, noting that the 1945 charter was negotiated by citizens "united in their commitment to work for peace."
Putin's escalation came after stunning Russian setbacks in the war, which has dragged on for more than six months. Biden, who has led efforts to isolate Russia and supply Ukraine with advanced weaponry, had already been planning to underscore those efforts in Wednesday's speech.
Putin's national address, which occurred after Biden had arrived in New York late Tuesday, caused White House aides to update some of the language in Biden's speech, according to an official. But a total rewrite wasn't necessary because White House officials had anticipated some of what Putin would say.
Ukrainian President Volodymyr Zelensky also planned to address the UN later on Wednesday.
After making his debut UN address last year under the cloud of a messy Afghanistan withdrawal and stalled domestic ambitions, Biden's aides believed he entered his sophomore outing with a stronger hand.
"We believe that the President heads to New York with the wind at his back," Sullivan told reporters at the White House on Tuesday, citing a mostly-united western alliance and recent wins on the domestic front, including a historic investment in fighting climate change.
Even as Biden proclaimed renewed US leadership Wednesday, deeper questions persist over his ability to maintain that position in the years ahead, as fears of a global recession looms and threats to American democracy fester.
Biden has spent ample time underscoring those threats in recent weeks, primarily for a domestic audience but with foreign capitals also listening intently. He has recounted in recent speeches sitting around a table at last year's Group of 7 summit in Cornwall, England, telling fellow leaders that "America is back."
French President Emmanuel Macron, Biden has told audiences, asked him: "For how long?"
That question still hangs over Biden's efforts on the world stage, even a year-and-a-half into his term, as his predecessor continues to wield influence over the Republican Party and prepares to mount another run for the White House. Biden himself said in an interview that aired Sunday that while he intends to run for reelection, a final decision "remains to be seen."
One of the issues currently at the forefront of global affairs -- the pained negotiations to restart the Iran nuclear deal, from which Trump withdrew -- only underscores the effects of pendulum swings in American leadership.
In his speech, Biden reiterated his stance that the US will not allow Iran to acquire a nuclear weapon as negotiations to revive a nuclear deal have failed to make significant progress in recent months.
"While the United States is prepared for a mutual return to the Joint Comprehensive Plan of Action if Iran steps up to its obligations, the United States is clear: We will not allow Iran to acquire a nuclear weapon," Biden said.
For Biden, the yearly UN speech was another stab at explaining to the world how he has steered the United States back into a position of leadership after the "America First" years of Donald Trump.
He called for expanding the United Nations Security Council, saying countries should refrain from using their veto powers except in rare circumstances.
"The United States supports increasing the number of both permanent and non-permanent" Security Council members, Biden said in his speech.
He said constant vetoes from countries on the Council were harming its effectiveness, and said only using vetoes in "rare, extraordinary situations" would ensure the council "remains credible and effective." Russia has consistently vetoed resolutions at the Security Council that have blocked action on Ukraine and other areas.
In his speech, Biden also announced $2.9 billion in US assistance to help address global food insecurity. The $2.9 billion investment, the White House said in a fact sheet, is aimed at shoring up food supply amid Russia's invasion of Ukraine, widespread inflation and other supply chain issues, and builds on $6.9 billion already committed by the US this year.
It includes $2 billion in global humanitarian assistance through USAID, the US Agency for International Development.
Later Wednesday morning, Biden will host a pledging session for the Global Fund to Fight HIV, AIDS, Tuberculosis and Malaria. In the evening, Biden and the first lady will host a leaders' reception at the American Museum of Natural History.
Biden and his aides have been drafting the address for several weeks, a period that coincided with Ukraine's successful counteroffensive taking back some Russian-held territory after months of occupation. The initiative had been coordinated with American officials, including through enhanced information and intelligence sharing, and sustained by weaponry provided by the US and its allies.
US officials have cautioned Ukraine's current gains don't necessarily signal a wider change in the outlook of the war, which remains likely to be a prolonged conflict. A day ahead of Biden's speech, two Russian-controlled regions in eastern Ukraine announced plans for referendums on officially joining Russia, votes the US has previously warned would be "shams."
One of Biden's objectives in his speech Wednesday was stressing the importance of maintaining unity among western allies in supporting Ukraine in the uncertain months ahead.
That effort is made more difficult by a looming energy crisis as Russia withholds supplies of natural gas to Europe as winter sets in. Higher costs spurred in part by withering western sanctions on Moscow have led to an economic calamity that is causing political turmoil for many leaders in Biden's coalition, including himself.
The President meets with one of those leaders, British Prime Minister Liz Truss, later Wednesday. It will be their first formal in-person talks since Truss entered office earlier this month following the decision of her predecessor, Boris Johnson, to step down.
She inherited a deep economic crisis, fueled by high inflation and soaring energy costs, that has led to fears the UK could soon enter a prolonged recession. While few in the Biden administration shed tears at Johnson's resignation -- Biden once described him as the "physical and emotional clone" of Trump -- the US and the UK were deeply aligned in their approach to Russia under his leadership.
White House officials expect that cooperation will continue under Truss, even as she comes under pressure to ease economic pressures at home.
Less certain, however, is whether Truss's hardline approach to Brexit will sour relations with Biden. The President has taken a personal interest in the particular issue of the Northern Ireland Protocol, a post-Brexit arrangement that requires extra checks on goods moving between Northern Ireland and the rest of the UK.
The rules were designed to keep the border between Northern Ireland and the Republic of Ireland open and avoid a return to sectarian violence. But Truss has moved to rewrite those rules, causing deep anxiety in both Brussels and Washington.
Putin is not attending this year's general assembly, though his foreign minister Sergey Lavrov was in New York for the event. Chinese President Xi Jinping also did not attend the UN in person this year.
The two autocratic leaders, who met in-person last week, have deepened ties between their countries as relations with the west deteriorate. Biden has warned Xi against supporting Putin in his invasion of Ukraine, a theme he's expected to reiterate in Wednesday's speech.
Biden said in his speech the US was not seeking "conflict" with China or other nations.
"We do not seek a cold war. We do not ask any nation to choose between the United States or any other partners," Biden said.
This story has been updated with further developments on Wednesday.