US President Donald Trump on Tuesday 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 a wide-ranging foreign policy speech that included scathing criticism of the United Nations and European nations, Trump made the case for lower levels of global migration and said world leaders should abandon efforts to fight climate change, which he called “the greatest con job” in the world.

In his first UN address since regaining power in January, Trump 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.

Trump 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."

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.

Some of his strongest language was reserved for migration as he lambasted the UN for "funding an assault" on Western nations.

"It's time to end the failed experiment of open borders," Trump said. "Your countries are going to hell," he said, also attacking London's Mayor Sadiq Khan, the first Muslim mayor of a Western capital.

He also used the major forum to denounce efforts to reduce global warming, calling climate change concerns "the greatest con job ever perpetrated on the world."

"What is the purpose of the United Nations?" asked Trump.

"All they seem to do is write a really strongly worded letter," he said. "It's empty words, and empty words don't solve war."

The 79-year-old even complained about a broken escalator and teleprompter at the New York headquarters of the UN, which he has repeatedly targeted during both of his presidential terms.

"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.

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.

Opening the annual summit, UN Secretary-General Antonio Guterres warned that aid cuts led by the United States were "wreaking havoc" in the world.

"What kind of world will we choose? A world of raw power – or a world of laws?" Guterres said. (Agencies)