US President Donald Trump warned Thursday that Washington would "take a pass" on talks to end the Ukraine war within days unless there is rapid progress from Moscow and Kyiv.

His comments came just hours after US Secretary of State Marco Rubio set the clock ticking, saying in Paris that the United States could "move on" from its role brokering the negotiations.

Trump has been pressing both sides for a truce, but has failed to extract any major concessions from the Kremlin despite an ice-breaking call with Russian President Vladimir Putin and repeated negotiations with Moscow.

"If for some reason one of the two parties makes it very difficult, we're just going to say: 'You're foolish. You're fools. You're horrible people' — and we're going to just take a pass," Trump told reporters in the Oval Office. 

"But hopefully we won't have to do that."

Republican Trump refused to cast blame on either Putin, who ordered the February 2022 full-scale invasion of pro-Western Ukraine, or Kyiv's President Volodymyr Zelensky, insisting both sides had to make progress.

But Trump warned that a decision on whether to abandon the talks could come "very shortly." "No specific number of days, but quickly. We want to get it done," he added.

'Move on'

Moscow has kept up strikes on Ukraine, killing at least two people and wounding dozens more in attacks on the northeastern regions of Kharkiv and Sumy, Ukrainian officials said.

One of the few commitments Trump had wrangled from Russia — a temporary moratorium on striking Ukrainian energy infrastructure — "expired" on Friday, Kremlin spokesman Dmitry Peskov said in response to an AFP question.

After meeting European officials in Paris to discuss a ceasefire, Rubio said Washington needed to figure out soon whether a ceasefire was "doable in the short term."

"Because if it's not, then I think we're just going to move on," he told reporters.

But speaking on a trip to Italy, US Vice President JD Vance still insisted he was "optimistic" about ending the three-year war.

Trump promised to end the war within 24 hours of taking office but has little to show for his efforts so far.

He has embarked on a rapprochement quest with the Kremlin that has alarmed Kyiv and driven a wedge between the United States and its European allies.

He and Vance also had a blazing Oval Office row in February with Zelensky, whom he still accuses of bearing responsibility for Moscow's invasion.

Trump insisted that he was not being "played" by Moscow, which is accused by Ukraine of dragging its feet.

"My whole life has been one big negotiation and I know when people are playing us and I know when they're not," the billionaire property tycoon added.

Asked if Putin was stretching out the process, Trump added, "I hope not. I'm going to let you know about that soon if he is... he's got a big force out there." 

'Mockery'

Zelensky meanwhile slammed the latest attacks on his country, which came just days before Easter.

Kyiv earlier announced it had received the bodies of 909 soldiers from Russia.

"This is how Russia started Good Friday — with ballistic missiles, cruise missiles, Shahed drones. A mockery of our people and cities," Zelensky said on Telegram.

Russia said it had hit "key drone production sites" and Ukrainian military airfields.

Putin last month rejected a joint US-Ukrainian proposal for a full and unconditional pause in the conflict, while the Kremlin has made a truce in the Black Sea conditional on the West lifting certain sanctions.

Trump has also repeatedly expressed anger and frustration at Zelensky in a marked break from his predecessor, Joe Biden.

Ukraine is set to sign a deal next week in Washington that would give the United States sweeping access to its mineral resources.

European powers have meanwhile been seeking a seat at the table in the negotiations, particularly as Trump's administration insists the continent should share the burden for Ukraine's security. 

France hosted meetings between US and European officials in Paris on Thursday, saying the talks had launched a "positive process."

The meetings included French President Emmanuel Macron, Rubio and US envoy Steve Witkoff.

Many allies have however been alarmed by Witkoff — who recently met Putin in Russia — repeating Moscow's talking points about the war.