New York, 19 September 2023 (dpa/MIA) - US President Joe Biden called on world leaders to "stand up" to Russia and support Ukraine's sovereignty in a forceful address to the UN General Assembly that also touched on Washington's tensions with China.

"Russia believes that the world will grow weary and allow it to brutalize Ukraine without consequence," he told an audience at the UN headquarters in New York that included Ukrainian President Volodymyr Zelensky.

"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 told the chamber the international community must "stand up to this naked aggression today to deter other would-be aggressors tomorrow."

This is the second UN General Assembly summit of world leaders to take place since Russia's all-out invasion of its neighbour in February 2022.

From Tuesday onwards, more than 140 prime ministers and heads of state will give speeches at the General Debate.

Zelensky, who is attending the event in New York in person for the first time since the the war erupted, is likely to attract the most attention - and attend a blizzard of sideline meetings.

He was due to address the assembly later on Tuesday.

Russian President Vladimir Putin will not attend the General Assembly, just like last year. Sergei Lavrov, Putin's foreign minister, will be his proxy once again.

Biden also touched on his administration's frictions with China.

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

"We will push back on aggression and intimidation, and defend the rules of the road," specifically naming freedom of navigation and potentially unfair trade practices.

"But we also stand ready to work together with China on issues where progress hinges on our common efforts," he said, mentioning the climate crisis.

Chinese President Xi Jinping is not scheduled to attend the meeting this year.

With rising geopolitical tensions among major economies, the US president appealed for greater unity and collaboration to tackle the biggest issues facing humankind.

"Our history need not dictate our future," he said, recalling his recent visit to Vietnam - a former bitter enemy that has become a strong trading partner of the United States.

"Adversaries can become partners, overwhelming challenges can be resolved, and deep wounds can heal," he told the packed General Assembly building.

Earlier, Brazilian President Luiz Inacio Lula da Silva was the first world leader to speak to the assembly.

Lula, who has refused to supply weapons to Ukraine, warned against attempts to divide the world into zones of influence and revive the Cold War.

"The war in Ukraine makes it clear that we are all incapable of enforcing the goals and principles of the UN Charter," he said. "Promoting a culture of peace is the duty of all of us."

A large portion of his speech was focussed on climate.

"The climate crisis is knocking on the door and destroying our homeland," the leader of Latin America's largest country said.

"People in poor countries are suffering particularly badly from climate change, which is largely caused by the developed world," Lula said.

He again called on rich countries to provide $100 billion per year for climate protection in developing countries, a longstanding pledge that has gone unfulfilled.