New York, New York - President Joe Biden on Tuesday warned the UN General Assembly against trying to "appease" Russia's "naked aggression" against Ukraine.

Ukrainian President Volodymyr Zelensky joined the annual UN General Assembly for the first time since the war and listened intently as Biden urged solidarity against Russia's invasion.

Russian President Vladimir Putin – who did not come to New York – is expecting that the world "will grow weary and allow it to brutalize Ukraine without consequence," Biden said.

"But I ask you this: if we abandon the core principles of the UN Charter to appease an aggressor, can any member state in this body feel confident that they are protected? If we allow Ukraine to be carved up, is the independence of any nation secure?" Biden said.

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"We must stand up to this naked aggression today to deter other would-be aggressors tomorrow."

Biden won applause from the chamber when he called for Ukraine's territorial integrity, but several prominent world leaders decided to miss this year's UN session, including from China, and allies Britain and France.

Zelensky is set to meet leaders less friendly to Ukraine's cause, including Brazil's President Luiz Inácio Lula da Silva, who has said previously that Ukraine shared blame for the war and faulted the billions of dollars in Western military aid to Kyiv.

Lula, who casts himself as a neutral mediator, told the General Assembly that "work needs to be done to create space for negotiations."

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"A lot is invested in weapons and very little in development," Lula said.

Zelensky, who until recently only traveled in utmost secrecy, will on Wednesday take part in a special session on Ukraine at the UN Security Council, where Russia is a permanent member wielding a veto over any binding actions. He is also due to stop in Washington.

Visiting a New York hospital treating wounded Ukrainian soldiers on Monday, Zelensky said that the United Nations still provides "a place for Russian terrorists."

Biden in his speech offered reassurances about the intense competition between the US and China, which has spurred warnings that the world could face a new Cold War.

"When it comes to China, I want to be clear and consistent. We seek to responsibly manage the competition between our countries, so it does not tip into conflict," Biden said.

Chinese Vice President Han Zheng met on the sidelines of the General Assembly on Monday with US Secretary of State Antony Blinken, in the second high-level meeting within days between the powers aimed at keeping tensions in check.

A few hours after Biden spoke, Zelensky used his address to try and solidify support for his country, warning that Russia poses a danger to the entire world. He said that Moscow's threat to use nuclear weapons was not the most frightening thing about the war against his country.

Russia was "weaponizing" essentials like food and energy, he said speaking in English in his first in-person trip to the UN in New York since the war began.

"These things are being used not only against our country, but against all of your countries. There are many conventions that limit the possession and proliferation of weapons, but there are no real restrictions on the use of food, energy, or other things as weapons."

Zelensky suggested Ukraine was fighting not only for its territorial integrity, but for values like freedom and human rights. He accused Russia of "genocide" over the kidnapping of Ukrainian children.

"While Russia is pushing the world to the final war, Ukraine is doing everything to ensure that after Russian aggression, no one in the world will dare to attack any nation."

He concluded: "War crimes must be punished. Deported people must come back home. The occupier must return to their own land."

Sergei Lavrov, Putin's foreign minister, will be Putin's proxy once again at the event.