Washington DC - President Donald Trump on Sunday lashed out at Vladimir Putin after Russia unleashed a devastating wave of attacks on Ukrainian cities.

"I've always had a very good relationship with Vladimir Putin of Russia, but something has happened to him. He has gone absolutely CRAZY!" Trump said in a post on Truth Social, as Moscow unleashed a record barrage of over 350 drones at Ukraine, killing at least 13 people.

"I've always said that he wants ALL of Ukraine, not just a piece of it, and maybe that's proving to be right, but if he does, it will lead to the downfall of Russia!" he added.

Trump also bizarrely chose to attack Ukrainian President Volodymyr Zelensky, accusing him of "doing his Country no favors by talking the way he does."

Donald Trump Trump sends warships to Venezuelan in alarming escalation of pressure on Maduro

Donald Trump Trump lashes out after judge makes significant ruling on Utah congressional map

"Everything out of his mouth causes problems, I don't like it, and it better stop," he wrote.

Earlier on Sunday, Trump told reporters that he was "not happy" with Putin over the latest Russian offensive.

"I've known him a long time, always gotten along with him, but he's sending rockets into cities and killing people, and I don't like it at all," said Trump on the tarmac at Morristown airport before boarding Air Force One bound for Washington.

Trump's remarks come as European allies and even some in his own Republican Party call for increased pressure on Russia to agree to a ceasefire.

The 78-year-old has avoided issuing ultimatums to Russia, instead threatening to walk away from negotiations if both sides cannot agree to a ceasefire.

But in response to a question on the tarmac in Morristown, Trump said Sunday he was "absolutely" considering increasing US sanctions on Russia in response to the latest violence.

Donald Trump Trump reacts to Russia's deadly strikes on Kyiv: "Not happy about this news"

Politicians MAGA Rep. Mike Collins caught on hot mic making big admission on Trump and Epstein files

"He's killing a lot of people. I don't know what's wrong with him. What the hell happened to him, right? He's killing a lot of people. I'm not happy about that."

The statement was at odds with Secretary of State Marco Rubio's testimony in Congress on Wednesday, when he said Trump believed that "right now, if you start threatening sanctions, the Russians will stop talking."

After a two-hour phone call with Putin last week, Trump said Moscow and Kyiv would "immediately start negotiations towards a ceasefire."

But the Russian leader has made no commitment to pause his three-year invasion of Ukraine, announcing only a vague proposal to work on a "memorandum" outlining Moscow's demands for peace.