U.S. Secretary of State Marco Rubio on Sunday said talks in Geneva about ending Russia's war on Ukraine had been "probably the most productive and meaningful meeting so far in this entire process."

Rubio gave the briefing standing with Andrii Yermak, the head of the Ukranian delegation and presidential chief of staff, after k meetings about U.S. President Donald Trump's peace proposal.

"Our teams have now gone to their rooms as we're working on some of the suggestions that were proffered to us, so we're working through making some changes, some adjustments, in the hopes of further narrowing the differences," Rubio said.

"I think this is a very, very meaningful, I would say probably best meeting and day we've had so far in this entire process going back to when we first came into office in January," Rubio added.

Ahead of the meetings with Rubio, top European and Ukrainian envoys conferred in Geneva on Sunday.

Earlier Sunday, Yermak wrote on social media that Ukraine's delegation had met with national security advisers from the U.K., France and Germany.

The allies have rallied around Kyiv in a push to revise the plan, which is seen as favoring Moscow.

Before the meeting, Trump on Sunday used a lengthy online post to blast Ukraine for a lack of gratitude for U.S. military assistance, while notably shying away from criticizing Russia.

Ukrainian President Volodymyr Zelenskyy said he was waiting for the outcome of the talks.

Rustem Umerov, secretary of Ukraine’s National Security and Defense Council and a member of Ukraine’s Geneva delegation, wrote that although the peace plan proposals were still be finalized, they included “many Ukrainian priorities.”