U.S. President Donald Trump said he was "dissatisfied" with Russian rival Vladimir Putin after Moscow launched the largest air strike on Ukraine.

Trump said in a rare condemnation: "What the hell is wrong with him? He killed a lot of people." Later he called Putin "absolutely crazy."

Ukrainian President Volodymyr Zelensky earlier said Washington's recent "silence" on Russia's attacks encouraged Putin, urging "strong pressure" on Moscow - including tougher sanctions.

At least 12 people were killed in Ukraine and dozens were injured in Ukraine after Russia opened fires 367 drones and missiles on Sunday, the highest figure in a night since Putin introduced a full-scale invasion in 2022.

Earlier on Monday, many parts of Ukraine once again warned of incoming drones and missiles.

Mayor Tirekov said at least three people were injured in the northeastern city of Kharkif.

"I've known him for a long time, always with him, but he's sending the rockets into the city and killing people, and I don't like it at all," Trump told reporters in New Jersey late Sunday.

Asked if he was considering increasing sanctions on Russia, Trump replied: "Absolutely." The U.S. president has threatened to do so many times before - but has not imposed any restrictions on Moscow.

Shortly thereafter, Trump wrote in a post about Truth Social that Putin was “absolutely crazy.”

"I kept saying he wanted all Ukraine, not just a part of it, maybe that's right, but if he did, it would lead to the fall of Russia!"

But the U.S. president also has strong words about Zelensky, saying he "does not help his country by talking about his own way."

"Everything in his mouth will cause problems, I don't like it, it's better to stop," Trump wrote.

While Kiev's European allies are imposing further sanctions for Russia, the United States says it will continue to try to facilitate these peace talks or “go away” if it doesn't follow up.

Last week, Trump and Putin made a two-hour phone call to discuss a US-promoted ceasefire deal to stop the fight.

The U.S. president said he believed the call was "good", adding that Russia and Ukraine would "start" negotiations on the ceasefire and "end the war."

Ukraine has publicly agreed to a 30-day ceasefire.

Putin only said Russia would work with Ukraine to produce a "memorandum" on "possible future peace" - a move described by Kiev and its European allies was a delay tactic.

The first direct Ukraine since 2022-Russian talks were held in Istanbul, Turkey on May 16.

Apart from a major prisoner-of-war exchange last week, the suspension was made even more closely with little progress.

Russia currently controls about 20% of Ukrainian territory. This includes Crimea-Ukraine's southern peninsula, annexed by Moscow in 2014.