US President Donald Trump warned Russia he is prepared to impose strong economic measures over the war in Ukraine and rejected a global move toward recognition of a Palestinian state, in a combative speech to the UN General Assembly.

In his first UN address since regaining power in January, Trump spoke to dozens of world leaders, many of whom have been alarmed to see the United States turn away from traditional alliances in favour of an isolationist "America First" policy.

Trump's warning to Russia came with a twist. He said he wants US allies to impose the same measures on Russia he is proposing to try to force Russian President Vladimir Putin to pull back from the biggest war in Europe since World War Two.

The US president has warned about the possibility of sanctions on Russia several times but has yet to follow through. Lately he has demanded Europe stop all Russian oil purchases before he will take action.

"In the event that Russia is not ready to make a deal to end the war, then the United States is fully prepared to impose a very strong round of powerful tariffs, which would stop the bloodshed, I believe, very quickly," he said.

But for the measures to be effective, he said, "European nations, all of you gathered here, would have to join us in adopting the exact same measures."

He planned a meeting later in the day with Ukrainian President Volodymyr Zelenskiy.

Dozens of world leaders gathered at the United Nations on Monday to embrace a Palestinian state, a landmark diplomatic shift that faces fierce resistance from Israel and its close ally the United States.

Trump rejected statehood for Palestinians, adopting the stance of Israeli Prime Minister Benjamin Netanyahu.

"The rewards would be too great for Hamas terrorists, for their atrocities," he said, repeating his call for the return of hostages taken by the Palestinian militant group.

Trump said the United States wants a ceasefire-for-hostages deal that would see the return all remaining hostages, alive and dead.

"We have to stop the war in Gaza immediately. We have to immediately negotiate peace," he said.

CRITICISM OF MIGRATION POLICIES

Trump argued that other world leaders should adopt his tough-on-migrants policy, touting his own efforts to arrest and deport migrants in the United States illegally, a stance that many countries around the world have viewed skeptically.

"It's destroying your country, and you have to do something about it on the world stage," he said.

Trump, who has cast himself as a peacemaker in a bid to win the Nobel Peace Prize, complained that the United Nations did not support his efforts to end conflicts around the world.

He twinned his complaint with a personal grievance about the UN's infrastructure, saying he and first lady Melania Trump were briefly marooned on a UN escalator and that his teleprompter was not initially working.

"These are the two things I got from the United Nations - a bad escalator and a bad teleprompter," Trump said, noting that Melania Trump nearly fell when the escalator stopped abruptly.

Since taking office again, Trump has upended US foreign policy, slashing foreign aid, imposing tariffs on friend and foe alike and cultivating warmer - if volatile - relations with Russia.

At the same time he has sought, so far with only limited success, to solve some of the world's most intractable conflicts.

Trump is among some 150 heads of state or government are expected to address the chamber this week. He spoke eight months into a second term marked by severe aid cuts that have sparked humanitarian worries and have raised doubts about the UN's future.

According to planning documents reviewed by Reuters, the Trump administration plans to call this week for sharply narrowing the right to asylum, seeking to undo the post-World War Two framework around humanitarian protection.

Trump's more restrictive stance would include requiring asylum-seekers to claim protection in the first country they enter, not a nation of their choosing, a State Department spokesperson said.

Guterres and Trump are expected to meet formally for the first time since Trump returned to office in January.