"If for some reason, one of the two parties makes it very difficult, we're just going to say, you're foolish," Trump told reporters Friday in the Oval Office. "You're fools, you're horrible people, and we're going to just take a pass. But hopefully we won't have to do that."

While Trump did not say he has a "specific number of days" in mind by which he wanted to see an agreement before walking away, he needed to see quick progress.

"I know when people are playing us, and I know when they're not," Trump said. "And I have to see an enthusiasm to want to end it. And I think I see that enthusiasm. I think I see it from both sides."

His comments followed a meeting of US officials, including Secretary of State Marco Rubio and US special envoy Steve Witkoff, with representatives from France, Germany and the UK in Paris on Thursday, where the US indicated its aim was to secure a full ceasefire in Ukraine within weeks, according to people familiar.

Following the meeting, Rubio said the US needed to see in "a matter of days" whether a deal was "doable in the short term.... because if it's not, then I think we're just going to move on," Rubio told reporters at Le Bourget airport outside of Paris on Friday morning, according to a transcript provided by the State Department.

Rubio also said the European nations could help "move the ball" to get a resolution and that their ideas had been "very helpful and constructive."

"We had a good meeting yesterday," he added. "But this isn't going to go on forever." The war in Ukraine "has no military solution to it" as "neither side has some strategic capability to end this war quickly", Rubio said.

Trump, who predicted on the campaign trail that he could quickly secure a ceasefire, hits the 100-day mark of his second stint in the White House on April 30. 

Trump "has dedicated a lot of time and energy to this, and there are a lot of things going on in the world right now that we need to be focused on," Rubio told reporters. "There are a lot of other really important things going on that deserve just as much if not more attention." 

Bloomberg reports that Thursday's talks in Paris also included a meeting between Witkoff and French president Emmanuel Macron and were attended by Ukrainian officials. US officials indicated they expected to make significant progress soon, and the participants agreed to work toward that. National security advisers and negotiators from Germany, France, the US and the UK plan to gather again in London next week to follow up on their discussions.