President Joe Biden said Wednesday that Russia has “shamelessly violated the core tenets" of the United Nations charter with its “brutal, needless war” in Ukraine.

Delivering a forceful condemnation of Russia's invasion to the international body, Biden said reports of Russian abuses against civilians in Ukraine “should make your blood run cold.” He also said Russian President Vladimir Putin's new nuclear threats against Europe showed “reckless disregard” for his nation's responsibilities as a signatory of the Treaty on the Non-Proliferation of Nuclear Weapons.

The address comes as Russian-controlled regions of eastern and southern Ukraine have announced plans to hold Kremllin-backed referendums in days ahead on becoming part of Russia and as Moscow is losing ground in the invasion. Russian President Vladimir Putin on Wednesday announced a partial mobilization to call up 300,000 reservists and accused the West of engaging in “nuclear blackmail.”

Biden is confronting no shortage of difficult issues as leaders gather this year.

In addition to the Russian war in Ukraine, European fears that a recession could be just around the corner are heightened. Administration concerns grow by the day that time is running short to revive the Iran nuclear deal and over China's saber-rattling on Taiwan.

When he addressed last year’s General Assembly, Biden focused on broad themes of global partnership, urging world leaders to act with haste against the coronavirus, climate change and human rights abuses. And he offered assurances that his presidency marked a return of American leadership to international institutions following Donald Trump’s “America First” foreign policy.

But one year later, global dynamics have dramatically changed.

Stewart Patrick, senior fellow and director of the Global Order and Institutions Program at the Washington think tank Carnegie Endowment for International Peace, wrote in an analysis that Biden’s task this year is “immense” compared to his first address to the U.N. as president.

“Last year, the U.S. leader won easy plaudits as the ‘anti-Trump,’ pledging that ‘America was back,’” Patrick said. “This year demands more. The liberal, rules-based international system is reeling, battered by Russian aggression, Chinese ambitions, authoritarian assaults, a halting pandemic recovery, quickening climate change, skepticism of the U.N.’s relevance, and gnawing doubts about American staying power.”

Beyond diplomacy, the president is also doing some politicking. This year's gathering comes less than seven weeks before pivotal midterm elections in the United States. Shortly after arriving in Manhattan on Tuesday night, Biden spoke at a Democratic National Committee fundraiser for about 100 participants that raised nearly $2 million, and he's set to hold another fundraiser on Thursday before heading back to Washington.

His Wednesday address comes on the heels of Ukrainian forces retaking control of large stretches of territory near Kharkiv. But even as Ukrainian forces have racked up battlefield wins, much of Europe is feeling painful blowback from economic sanctions levied against Russia. A vast reduction in Russian oil and gas has led to a sharp jump in energy prices, skyrocketing inflation and growing risk of Europe slipping into a recession.

Biden's visit to the U.N. also comes as his administration's efforts to revive the 2015 Iran nuclear deal appears stalled.

The deal brokered by the Obama administration — and scrapped by Trump in 2018 — provided billions of dollars in sanctions relief in exchange for Iran’s agreement to dismantle much of its nuclear program and open its facilities to extensive international inspection.

Sullivan said no breakthrough with Iran is expected during the General Assembly but Biden would make clear in his speech that a deal can still be done "if Iran is prepared to be serious about its obligations." He added that administration officials would be consulting with fellow signatories of the 2015 deal on the sidelines of this week's meetings.

This year's U.N. gathering is back to being a full-scale, in-person event after two years of curtailed activity due to the pandemic. In 2020, the in-person gathering was canceled and leaders instead delivered prerecorded speeches; last year was a mix of in-person and prerecorded speeches. Biden and first lady Jill Biden were set to host a leaders' reception on Wednesday evening.

China's President Xi Jinping opted not to attend this year's U.N. gathering, but his country's conduct and intentions will loom large during the leaders' talks.

Last month, the U.N. human rights office raised concerns about possible “crimes against humanity” in China's western region against Uyghurs and other largely Muslim ethnic groups. Beijing has vowed to suspend cooperation with the office and blasted what it described as a Western plot to undermine China’s rise.

Meanwhile, China’s government on Monday said Biden’s statement in a CBS “60 Minutes” interview that American forces would defend Taiwan if Beijing tried to invade the self-ruled island was a violation of U.S. commitments on the matter, but it gave no indication of possible retaliation.

The White House said after the interview that there has been no change in U.S. policy on Taiwan, which China claims as its own. That policy says Washington wants to see Taiwan’s status resolved peacefully but doesn’t say whether U.S. forces might be sent in response to a Chinese attack.