US President Donald Trump blasted the United Nations and Europe on his return to the world body Tuesday, warning that Western countries were "going to hell" because of migration and calling climate change a "con job."

In a blistering speech during his first UN General Assembly appearance since his White House comeback, Trump also accused the world body of failing to help him as he tried to broker a series of peace deals including in Gaza and Ukraine.

"What is the purpose of the United Nations?" asked Trump in a wide-ranging speech lasting nearly an hour. "It has such tremendous potential but it's not even coming close to living up to that."

Trump's first speech to the UN back in 2018 saw fellow leaders laughing at the Republican, but this time his full-frontal attack on the global organization and US allies was received in near total silence.

The 79-year-old's litany of complaints even extended to 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," he said.

'Going to hell'

Trump began his speech by criticizing the UN for failing to get involved in what he claims are seven wars that he has ended, or in his failed efforts to end Russia's invasion of Ukraine and Israel's war in Gaza.

"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."

He then called recognition by a slate of Washington's allies of a Palestinian state a "reward" to Hamas for "horrible atrocities " in the armed group's October 7, 2023 attack on Israel.

Trump had more harsh words for European allies for failing to stop oil purchases from Russia. He criticized China and India on the same score -- but Moscow itself escaped relatively lightly.

His strongest language was reserved for blasting migration, one of the core political messages that has driven his two US election victories.

Trump lambasted the UN for "funding an assault" on Western nations that he described as an "invasion."

"Your countries are going to hell," he told European leaders.

The US president took a typically controversial stance on climate change too, calling it a "hoax" made up by "evil people." He has pushed for oil drilling and rolled back environmental protections since returning to office.

"Climate change -- it's the greatest con job ever perpetrated on the world," said Trump. 

'Wreaking havoc'

Trump boasted of his tough crime policies, including sending troops to Washington and deadly US strikes on alleged Venezuelan drug smuggling boats.

"To every terrorist thug smuggling poisonous drugs into the United States of America, please be warned that we will blow you out of existence," Trump said.

Trump's second term has opened with a blaze of nationalist policies curbing cooperation with the rest of the world.

He has moved to pull the United States out of the World Health Organization and the UN climate pact, severely curtailed US development assistance and wielded sanctions against foreign judges over rulings he sees as violating sovereignty.

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

Brazilian President Luiz Inacio Lula da Silva meanwhile warned in his speech of "anti-democratic forces" targeting institutions after an alleged coup plot orchestrated by his predecessor, who has won backing from Trump.

Trump however said he and Lula shared a brief hug at the UN and had agreed to meet next week.

On Ukraine, Trump will meet President Volodymyr Zelensky for the second time since he sat down in Alaska with Russian President Vladimir Putin in August -- a summit that broke Moscow's isolation in the West but yielded no progress.

Ahead of Trump's speech, the US Secret Service said they had disrupted a plot to potentially disrupt telecommunications around the UN that involved "nation-state threat actors."