The U.S. has made “progress” on securing a peace deal between Ukraine and Russia, but there is still a “ways to go,” Secretary of State Marco Rubio told reporters on Friday.

“I think we’ve made progress, but we have a ways to go. And obviously the hardest issues are always the last issues,” Rubio said at the State Department briefing, noting that the ultimate agreement will have to come from both sides.

“Maybe that happens this week, maybe that happens next month, maybe that’s not ready for a few months,” he says on the timeline of the deal, which he also offered simply may “not be possible.”

Rubio’s remarks strike a more cautious tone about the likelihood of a deal being imminent than ones made recently by President Donald Trump, who on Tuesday called a peace deal “closer than ever” after U.S. talks with Ukrainian officials in Berlin earlier this week..

Russian officials are set to continue discussions on the latest peace deal draft with peace envoy Steve Witkoff and Trump’s son-in-law Jared Kushner in Miami this weekend. While all sides have indicated that talks thus far have made headway, outstanding issues remain, including on the fate of the Donbas region and security guarantees for Ukraine, as the war nears its fourth year.

The secretary also stressed that the U.S. is still trying to figure out what Russia and Ukraine are willing to compromise on, and that the negotiation partly relies on timing related to when both sides can come together.

On Donbas, which houses strategic military equipment for Ukraine and makes up its front line, Ukrainian President Volodymyr Zelenskyy said he would agree to a “free economic zone” not controlled by Russia in the 15 percent of area currently controlled by Ukraine.

But the Kremlin has signaled that it sees Donbas as being fully a part of Russia, with Russian President Vladimir Putin saying the military would take the remaining part of Donbas “by force” if necessary.

Russia has also refused the possibility of Western military troops being present in Ukraine, despite the U.S. offering Ukraine “Article 5-like” security guarantees that Zelenskyy showed openness to.

Zelenskyy views Western security guarantees as the most important part of the deal, necessary to prohibit further Russian aggression. For Russia, officials have stressed that any NATO-like guarantees are not on the table.

Putin remained belligerent Friday in the wake of the coming Miami talks during his four-and-a-half-hour press conference, boasting about Russian military advancement in Ukraine and scoffing at the idea of starting new conflicts in Europe – but only if countries begin respecting Russia.

“There won’t be any operations if you treat us with respect, if you respect our interests just as we’ve always tried to respect yours,” Putin said.

The Russian leader didn’t offer any new compromises in his press briefing, and maintained that the “root causes” of the war would have to be addressed, in line with his previous remarks.