Both President Trump and Secretary of State Marco Rubio warned Friday that the US would “move on” from trying to make peace between Russia and Ukraine unless there are clear signs in “a matter of days” that an agreement to end the fighting can be reached .

“We’re not going to continue with this endeavor for weeks and months on end,” Rubio said after landmark meetings in Paris with European and Ukrainian leaders.

“So we need to determine very quickly now, and I’m talking about a matter of days, whether or not this is doable in the next few weeks,” he added.

“If it’s not possible, if we’re so far apart that this is not going to happen, then I think [President Trump] is probably at a point where he’s going to say, ‘Well, we’re done.'”

Trump backed his top diplomat during an afternoon question-and-answer session with reporters in the Oval Office, saying “Marco was right.”

“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,’” the president said. “But hopefully we won’t have to do that.”

The president also declined to say whether he would continue to support Kyiv if the diplomatic stalemate continues, saying: “I’m not going to say that because I think we’re going to get it done.”

White House officials, including Trump himself, have expressed frustration in recent weeks over the lack of progress toward ending Europe’s bloodiest conflict since World War II, with Russia keeping up attacks on Ukrainian civilians and infrastructure in defiance of announced agreements.

However, the secretary of state hinted that the US was leaning toward easing up on current sanctions, telling reporters that Europe is “going to have to be involved” with the peace process because “many of (the Russian sanctions) are European sanctions that we can’t lift, if that were ever to be part of a deal.”

“It’s not our war. We have other priorities to focus on,” Rubio added. “The president feels very strongly about that. He has dedicated a lot of time and energy to this … this is important, but there are a lot of other really important things going on that deserves just as much, if not more attention.”

The threat by Trump and Rubio caused alarm among veteran national security hands, one of whom warned the ultimatum “could have a perverse effect in the Kremlin.”

“Injecting a sense of urgency into talks is a good thing,” said the Foundation for Defense of Democracy’s John Hardie before adding: “I think we’d be better off focusing on applying pressure on Russia, which is the obstacle to peace.” 

“The Kremlin’s ideal scenario is to get the US to kind of press Ukraine to a deal that’s very favorable to Russia,” Hardie went on. “But perhaps their next best alternative is just for us to kind of wash his hands and walk away,” he said. “I think their expectation would be that US aid for Ukraine would evaporate, and knowing Trump — I hope that would not happen — but there’s a good chance it would.

“If that happens, the chances of reaching any sort of deal directly between the Ukrainians and Russians, perhaps with some sort of European mediation, are pretty slim.”

“Many Ukrainians never believed in the possibility of success of peace talks with Russia from the start because Russia understands only strength and only force,” added Kyiv-based Center for European Policy Analysis fellow Elena Davlikanova. “So in our opinion, the best way to come to peace as soon as possible is to provide Ukraine with as much weapons as possible [and] to continue provide intelligence.”

When asked about Rubio’s comments, Kremlin spokesman Dmitry Peskov told reporters Friday that “fairly complex” negotiations are ongoing between Russia and the US.

“Russia is striving toward resolving this conflict, securing its own interests, and is open to dialogue. We are continuing to do this,” he said.

Peskov added that no direct talks between Trump and Russian President Vladimir Putin are scheduled in the coming days.