U.S. Secretary of State Marco Rubio said roughly four-hour talks with a Ukrainian delegation in Florida on Sunday made "additional" progress on a revised peace plan to end the Ukraine crisis, but "there is more work to be done."

"This is delicate, it's complicated," Rubio told reporters after the meeting. "There are a lot of moving parts, and obviously there's another party involved here that will have to be a part of the equation."

"We don't just want to end the war, we also want to help Ukraine be safe forever," said the top U.S. diplomat.

Rustem Umerov, secretary of Ukraine's National Security and Defense Council, described the talks as "difficult but productive."

"We have made tangible progress toward establishing a just peace," Umerov, who heads the Ukrainian negotiating team, wrote on Facebook.

The meeting was meaningful and successful, he wrote, adding that there is still a lot of work ahead and the two sides will continue consultations and coordination on further steps for the sake of peace in Ukraine.

The latest round of talks between the two sides was held in Hallandale Beach, the U.S. state of Florida earlier in the day. Neither Rubio nor Umerov took questions from reporters after the meeting.

U.S. presidential special envoy Steve Witkoff and U.S. President Donald Trump's son-in-law Jared Kushner also joined Sunday's talks and will fly to Moscow on Monday for further discussions, according to a Wall Street Journal report.