LONDON — Ukrainian President Volodymyr Zelenskyy praised his “productive meeting” with U.S. President Donald Trump on the sidelines of the United Nations General Assembly on Tuesday, after which Trump appeared to jettison his long-held skepticism of Kyiv’s battlefield ambitions.

Shortly after the meeting, Trump wrote on social media, “After getting to know and fully understand the Ukraine/Russia Military and Economic situation and, after seeing the Economic trouble it is causing Russia, 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.”

The statement marked a dramatic pivot away from the White House’s established position that Kyiv will not be able to liberate the 20% or so of its internationally-recognized territory occupied by Russian forces since 2014.

Trump has repeatedly suggested that Zelenskyy will have to cede — or “swap” — some territory to achieve a peace deal with Russian President Vladimir Putin, telling the Ukrainian president at a fractious February Oval Office meeting, “You don’t have the cards.”

But on Tuesday, the president appeared to have changed his tune. “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?” Trump wrote.

“Russia has been fighting aimlessly for three and a half years, a war that should have taken a Real Military Power less than a week to win,” he continued, suggesting Moscow was a “paper tiger” citing its battlefield failures.

Kremlin spokesperson Dmirty Peskov disputed Trump’s comments, telling the RBC news agency on Wednesday, “Russia is not a tiger; Russia is more closely associated with a bear. There are no paper bears. Russia is a real bear.”

Peskov also rejected Trump’s suggestion that the Russian economy was struggling. “Let’s not forget that the world has entered a stage of completely unpredictable macroeconomic conditions,” he told RBC.

“The ability to conduct economic analysis has disappeared globally,” Peskov said. “If I were an economic analyst, I’d look for another job, because it’s impossible to predict.”

On Tuesday, Zelenskyy said in a post to Telegram that he was “grateful to President Trump for strong cooperation with the United States.”

“The president clearly understands the situation and is well informed about all aspects of this war,” Zelenskyy added. “We highly appreciate his determination to help end this war.”

Speaking to reporters after the meeting, Zelenskyy described Trump’s pivot as “a big shift, a really big shift.”

Asked if the social media post by Trump is a “game changer” for the war, Zelenskyy responded: “Trump is a game changer by himself.”

Zelenskyy added that he thinks the president is now aware of “more details” of what is happening on the battlefield, and suggested that U.S. intelligence on the situation is aligned with Ukraine’s.

Zelenskyy also said it was “good news” that Russia’s economy is struggling amid the strains of its full-scale invasion, but that it was “bad news” that Moscow still has the resources to fund its war.

“Trump agreed with me that Putin won’t wait for the war in Ukraine to end,” he added. “He will try to exploit weak places in Europe, in NATO countries, he will try to do it.”

Oleksandr Merezhko, a member of the Ukrainian parliament representing Zelenskyy’s party and chair of the body’s foreign affairs committee, told ABC News he saw Trump’s statement as a “pleasant surprise, giving some hope that he finally is starting to view Russia’s war against Ukraine in a different light.”

“At the same time, knowing how often Trump might change his stance, we should be cautiously optimistic,” Merezhko added. “What matters are his actions, concrete steps to help Ukraine, not only rhetoric, however good it might be.”

“Trump’s statement implies that the U.S. will continue to sell weapons to the European and NATO countries for Ukraine,” he added. “And also it can be inferred from this statement that Ukraine won’t be restricted in the use of American weaponry in the territory of Russia.”

Oleksiy Goncharenko, a prominent opposition member of parliament, was less sanguine.

“Trump’s statement is not about Ukraine’s victory, it is about washing hands of the war,” he wrote on Telegram. “He directly says: ‘You deal with the EU there. I hope you succeed. Good luck to everyone!'”

“Obviously, right now Russia does not want to stop,” Goncharenko added. “But our task is not to risk the lives of hundreds of thousands, but to be on the defense.”

“The reality is that we are neither losing nor winning,” he continued, warning that embarking on a costly “war of attrition” would be “idiocy.”

ABC News’ Karen Travers, Michelle Stoddart, Hannah Demissie and Mariam Khan contributed to this report.