Donald Trump has warned that if Vladimir Putin attempts to conquer all of Ukraine, it will lead to the “downfall” of Russia, while also criticising Volodymyr Zelenskyy in a Sunday night post on Truth Social.

“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 wrote in a social media post, adding, “He is needlessly killing a lot of people, and I’m not just talking about soldiers.”

Earlier on Sunday the US president told reporters that was he was “very surprised” that his Russian counterpart had intensified the bombardment of Ukrainian cities despite the US president’s efforts to broker a ceasefire.

Pressed by a reporter to say if he was now seriously considering “putting more sanctions on Russia”, Trump replied: “Absolutely. He’s killing a lot of people. What the hell happened to him?”

In his post on Sunday night, Trump also criticised Zelenskyy, saying the Ukrainian president was “doing his Country no favors by talking the way he does.”

“Everything out of his mouth causes problems, I don’t like it, and it better stop.”

Earlier on Sunday, Zelenskyy condemned “the silence of America” after Russia carried out its largest air raid in three years of war, with a second straight night of massive drone and ballistic missile strikes killing at least 12 people, including three children on Saturday into Sunday.

Ukrainian officials confirmed Moscow had launched 298 drones and 69 missiles in multiple waves on sites across the country.

“Every such terrorist Russian strike is reason enough for new sanctions against Russia,” Ukraine’s president said.

During his campaign for the presidency, Trump repeatedly claimed that if elected, he would end the war in Ukraine in 24 hours, even before being inaugurated.

However, the intensity and frequency of this weekend’s strikes contrasted sharply with Trump’s claim that Vladimir Putin was interested in peace.

The attacks meant Kyiv Day – celebrated on the last Sunday in May – began with exhausted people sheltered in bunkers, metro stations and basements.

Ukraine and its European allies have sought to push Moscow into signing a 30-day ceasefire as a first step to negotiating an end to the war. In a blow to their efforts, Trump this week declined to place further sanctions on Moscow for not agreeing to an immediate pause in fighting, as Kyiv had wanted.

Zelenskyy’s chief of staff, Andriy Yermak, wrote on Telegram: “Without pressure, nothing will change and Russia and its allies will only build up forces for such murders in western countries. Moscow will fight as long as it has the ability to produce weapons.”