US President Joe Biden addressed world leaders at the United Nations for the final time on Tuesday, declaring that Russia's war in Ukraine has failed and that a diplomatic solution between Israel and Lebanon's Hezbollah was still possible.

With four months left in office, Biden stepped up to the green-marbled lectern at the UN General Assembly with wars in Ukraine, the Gaza Strip and Sudan still raging and likely to outlast his presidency, which ends in January.

He sought to calm tensions as the nearly year-long war between Israel and Hamas in the besieged Gaza Strip now threatens to engulf Lebanon - where Israel targeted more than a thousand Hezbollah targets on Monday.

"Full scale war is not in anyone's interest, even if situation has escalated, a diplomatic solution is still possible," he told the 193-member UN General Assembly.

To a round of applause, Biden called on Israel and Hamas to finalise the terms of a Gaza ceasefire and hostage release deal put forward by the US, Qatar and Egypt.

Biden's presidency has also been dominated by Russia's February 2022 invasion of Ukraine. Ukrainian President Volodymyr Zelenskiy was in the assembly hall to hear Biden speak and emphasise US support for his country.

"The good news is Putin's war has failed at his core aim. He set out to destroy Ukraine, but Ukraine is still free," said Biden.

"We cannot grow weary, we cannot look away, and we will not let up on our support for Ukraine, not until Ukraine wins with a just, durable peace," he said.

Biden is due to hear from Zelenskiy about a new Ukrainian peace plan when they meet in Washington on Thursday. A US official said the plan is probably much like previous plans calling for more weaponry and support for Ukraine's fight.

Biden said on Tuesday that progress toward peace in the Middle East would put the world in a stronger position to do "with the ongoing threat posed by Iran."

He said the United States was seeking to responsibly manage competition with China so it does not veer into conflict.

"We stand ready to cooperate on urgent challenges," he said. "We recently resumed cooperation with China to stop the flow of deadly synthetic narcotics. I appreciate the collaboration. It matters for the people of my country and many others around the world."

Biden also had strong words for the leaders of Sudan's warring parties: "End this war now."