US President Donald Trump has said that Ukraine could win back all of its territory from Russia - and even go further - in a major pivot after meeting Ukrainian President Volodymyr Zelensky.
The astonishing turnaround came shortly after Mr Trump also called for NATO countries to shoot down any Russian jets that violate their airspace.
"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," Mr Trump said on his Truth Social network after his talks with Mr Zelensky.
Mr Trump also said Russia was "fighting aimlessly" after three years of war, in an apparent change of heart just over a month after he met Russian President Vladimir Putin in Alaska.
The US president has previously shown lukewarm support for Mr Zelensky, with whom he had a huge televised Oval Office bust-up in February during which he told the Ukrainian "you don't have the cards" to win.
But in his social media post, Mr Trump dismissed Russia as a "paper tiger," saying that "Putin and Russia are in BIG Economic trouble, and this is the time for Ukraine to act."
"With time, patience, and the financial support of Europe and, in particular, NATO, the original Borders from where this War started, is very much an option. Why not?" Mr Trump wrote.
He added that as Russia's economy gets worse "Ukraine would be able to take back their Country in its original form and, who knows, maybe even go further than that!"
'Escalation trap'
During his meeting at with Mr Zelensky on the margins of the UN General Assembly, Mr Trump said he had "great respect for the fight that Ukraine is putting up. It's pretty amazing actually."
Mr Zelensky thanked Mr Trump for his "personal efforts to stop this war" and echoed Mr Trump's call for European countries to stop buying Russian oil.
And after a series of recent incursions by Russian fighter jets and drones that have rattled Washington's NATO allies in Europe, Mr Trump said they would be within their rights to act.
"Yes I do," Mr Trump said when a reporter asked if NATO countries should shoot down Russian aircraft if they enter their airspace.
Mr Trump however deflected questions about whether he believed Mr Putin was still a reliable negotiating partner despite Moscow's continued attacks on Ukraine.
"I'll let you know in about a month from now, okay?" Mr Trump said when asked if he still trusted Mr Putin.
The 79-year-old Republican has previously, and repeatedly, given deadlines of two weeks to make a decision on whether to take steps including fresh sanctions against Russia.
Tensions between Russia and Europe over Ukraine have escalated with the recent spate of aerial violations.
NATO scrambled jets after three Russian MiG-31 fighters on Friday breached Estonian airspace for some 12 minutes, prompting Estonia to call for a meeting of the UN Security Council and talks with NATO allies.
Fellow NATO member Poland said earlier this month that Russian drones had repeatedly violated its airspace during an attack on Ukraine, in what Warsaw called an "act of aggression."
Germany reacted cautiously to Mr Trump's comments on shooting down Russian planes, highlighting the need to avoid an "escalation trap."
"Level-headedness is not cowardice and not fear, but a responsibility towards your own country and towards peace in Europe," German defence minister Boris Pistorius said.
EU chief Ursula von der Leyen said she discussed Russia's airspace violations with Mr Trump at the UN, and agreed on the need to cut Moscow's energy revenues.
Russia plans to expand operations deeper into Kharkiv
Russia has said it had captured a large part of the northeastern Ukrainian city of Kupiansk and that it wanted to expand its advance much deeper into the Kharkiv region.
"Control over Kupiansk will allow for further advances deep into the Kharkiv region, including towards Izium and Chuguiv," the Russian army said in a statement.
Kharkiv is not among the five regions of Ukraine that Russia claims to have annexed, as its troops were largely pushed out of the region in a successful counteroffensive by Kyiv's forces in 2022.
Russia's latest statement appears to show it has not abandoned its territorial ambitions in the region.
The Russian army said it controlled more than 65 percent of the buildings in Kupiansk.
Ukrainian President Volodymyr Zelensky told journalists last week that Kyiv was still battling for control of the city.
"In the Kupiansk area, intense actions are ongoing, and there are appropriate forces there," he said.
Kupiansk, an important transport hub, was initially captured by Russian forces in the first months of the assault before being retaken by Ukraine.
Russia says taking the town will help it advance in the neighbouring Donetsk region.
