US President Donald Trump said late on Sunday he is "not happy with what Putin's doing," after Moscow launched its biggest aerial strike of the all-out war on Ukraine overnight.
Russian President Vladimir Putin has "gone absolutely crazy," Trump added.
"He's killing a lot of people. And I don't know what the hell happened to Putin," Trump told reporters before boarding Air Force One in Morristown in New Jersey, as he prepared to return to Washington.
"I've known him a long time. Always gotten along with him. But he's sending rockets into cities and killing people. And I didn't like it at all," Trump said, adding that attacks happened while he and his Russian counterpart were "in the middle of talking".
He added he would "absolutely" consider additional sanctions against Russia, a measure Ukrainian President Volodymyr Zelenskyy has pushed for.
Moscow launched a barrage of drones and missiles in back-to-back strikes on cities and villages across Ukraine, including its capital Kyiv, killing at least 12 and injuring dozens.
On Sunday, Ukraine's Air Force said Russia launched 367 drones and missiles at the country overnight, making it the largest single aerial attack since the start of Russia's full-scale invasion of Ukraine.
When asked by a reporter if he would potentially impose additional sanctions on Russia, Trump said he would "absolutely" consider doing so.
Trump extends deadline for EU tariffs
Speaking on tariffs, the US President said he will postpone the implementation of a 50% tariff on goods from the European Union from June 1 until July 9.
Trump said that after a "good call" with European Commission President Ursula von der Leyen, he agreed to move the date to buy time for negotiations with the bloc.
Trump had threatened with the 50% tax on all imports from the European Union in a social media post on Friday, and had said the 27-member bloc which "was formed for the primary purpose of taking advantage of the United States" had been "very difficult to deal with" on trade and that negotiations were "going nowhere".
EU Commissioner for Trade and Economic Security Maroš Šefčovič responded to Trump's threat by reiterating the bloc's commitment to securing a trade deal that "works for both" and is based on "respect, not threats".
