Top Ukrainian envoys met with U.S. Secretary of State Marco Rubio in Geneva Sunday to discuss U.S. President Donald Trump’s proposal to end Russia’s war on Ukraine.

Speaking to journalists, Rubio described that first session of talks as “probably the most productive and meaningful meeting" since the Trump administration came to power.

He also said that both delegations would meet again in a second meeting later on Sunday night.

Russia will also need to approve the final peace plan, Rubio said.

The head of the Ukrainian delegation, presidential chief of staff Andrii Yermak, also confirmed an initial session of talks had concluded and that a second meeting would soon take place.

“I want to confirm that we had a very productive first session with the distinguished American delegation. We have made very good progress and are moving forward to a just and lasting peace,” he said.

“Very soon today the second meeting will take place, where we will continue to work on joint proposals with the engagement of our European partners. Final decisions will be taken by our Presidents.”

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.

After Trump's post, Ukrainian President Volodymyr Zelenskyy said he was “grateful” for U.S.-led efforts on security, but stressed that “the crux of the entire diplomatic situation is that it was Russia, and only Russia, that started this war.”

The 28-point blueprint drawn up by the U.S. to end the nearly four-year war has sparked alarm in Kyiv and European capitals.

Zelenskyy has said his country could face a stark choice between standing up for its sovereign rights and preserving the American support it needs.

The proposal, originating from negotiations between Washington and Moscow, acquiesces to many Russian demands that Zelenskyy has categorically rejected on dozens of occasions, including giving up large pieces of territory.

The Ukrainian leader has vowed that his people “will always defend” their home.

Before convening with U.S. officials, Yermak and his team also 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.