US President Donald Trump said Tuesday that Ukraine could win back all of its territory from Russia, in an astonishing turnaround on the war after meeting President Volodymyr Zelensky.

Trump's suggestion that Kyiv could win, with financial support from EU and NATO, marks an extraordinary shift after months of saying Ukraine would likely have to cede land to its larger neighbor.

Zelensky hailed Trump's comments as a "big shift."

In a further jibe at Moscow, he also called for NATO countries to shoot down any Russian fighter jets violating their airspace, following a series of incidents that have rattled US allies in Eastern Europe.

"I think Ukraine, with the support of the European Union, is in a position to fight and WIN all of Ukraine back in its original form," Trump said in a Truth Social Post after meeting Zelensky at the United Nations.

Trump added that on top of being able to take back the country in its original form, Kyiv could "maybe even go further than that!" -- although he did not elaborate on what he meant.

'BIG economic trouble'

The US leader's comments mark the latest in a series of reversals on Ukraine, including a sudden pivot to peace talks with Russian President Vladimir Putin early this year that stunned allies.

Trump had also shown lukewarm support for Ukraine, telling Zelensky during a televised Oval Office bust-up in February that "you don't have the cards" to beat Russia.

But his new shift reflected his growing frustration with Putin since a summit in Alaska on August 15 failed to produce a breakthrough, and was instead followed by increased Russian attacks. 

Trump told reporters on Tuesday that he had counted on a bond with Putin to bring an end to the three-and-a-half-year-old war -- but "unfortunately, that relationship didn't mean anything."

In his post, Trump said he had changed his view on the war "after getting to know and fully understand the Ukraine/Russia Military and Economic situation and, after seeing the Economic trouble it is causing Russia."

"Putin and Russia are in BIG Economic trouble, and this is the time for Ukraine to act," Trump said.

He added that Russia was "fighting aimlessly" after more than three years of war and was now a "paper tiger" instead of a serious nuclear force.

'Good luck to all!'

Amid astonishment in Europe about Trump's sudden shift, there were concerns in some capitals that the US president's message may not have been quite what it seemed.

The references to EU and NATO, combined with his closing comment "Good luck to all!", led to fears that he may be trying to wash his hands of a conflict that he blames on his predecessor Joe Biden.

Trump, who has repeatedly pushed NATO to take more of the burden for supporting Ukraine, insisted Washington would continue to give NATO weapons "to do what they want with them."

Trump's announcement came shortly after Zelensky briefed him on what he said were Ukraine's recent military successes against Russia, despite Moscow's grinding advances in the east of the country.

"This post of Trump is a big shift," Zelensky said in a press conference.

Zelensky meanwhile, raised the alarm over Russia's recent drone intrusions into NATO nations, saying Putin was probing the "weak places" in the alliance's defenses.

Trump said NATO forces would be within their rights to act.

"Yes I do," Trump said when a reporter asked if NATO countries should shoot down Russian aircraft if they enter their airspace.

Recent incidents include NATO scrambling jets after three Russian fighters on Friday breached Estonian airspace, and Poland saying earlier this month that Russian drones had repeatedly crossed into its territory during an attack on Ukraine.

by Gregory Walton with Danny Kemp in Washington