Moscow, Russia - Russia said Wednesday it would press on with its war on Ukraine and laughed off President Donald Trump's claim that Kyiv's army could retake territory it had seized.

Moscow also pushed back on Trump's characterization of Russia as a "paper tiger," a day after he dismissed Russia's army and said he could see Ukraine winning back every inch of land captured by Russia's forces.

Trump's remarks, delivered after a meeting with Ukrainian President Volodymyr Zelensky at the UN, were a major pivot in his stance on the three-and-a-half-year conflict, which he had at one point boasted he could end within hours.

But the Republican has for weeks voiced mounting frustration with Putin for refusing to halt his offensive.

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"We are continuing our special military operation to ensure our interests and achieve the goals" set by Putin, said Kremlin spokesperson Dmitry Peskov, using Moscow's term for its assault on Ukraine.

"We are doing this for both the present and the future of our country. For many generations to come. Therefore, we have no alternative," he added in a radio interview.

Moscow's army controls around one-fifth of Ukraine's territory, including the Crimean peninsula annexed in 2014, and has been grinding forwards on the battlefield, with both armies suffering immense losses.

Trump had on Tuesday mocked Russia's inability to quickly beat Ukraine.

In a post on Truth Social, he said Ukraine may "be able to take back their Country in its original form and, who knows, maybe even go further than that."

The Kremlin hit back, with Peskov telling reporters: "The idea that Ukraine can recapture something is, from our point of view, mistaken."

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He added: "The phrase 'paper tiger' was used in relation to our economy. Russia is more associated with a bear. And paper bears don't exist. Russia is a real bear."

Peskov also dismissed claims that Russia breached NATO's airspace as "hysteria", after Trump said the allies should shoot down Russian jets if they violate their territory.

NATO countries say multiple Russian fighter jets and drones have violated European member states' airspace in recent weeks, accusing Moscow of testing the alliance's boundaries.

With peace progress on Ukraine stalled, Peskov said a broader reconciliation between Moscow and Washington ushered in when Trump returned to the White House in January has yielded "close to zero" results.

Zelensky has hailed Trump's apparent change of position as a "big shift", though it is unclear if the US leader will follow through with concrete steps, such as more sanctions on Russia.