LONDON — U.S., Ukrainian and European officials are due to meet in Switzerland on Sunday for talks on the contentious American-Russian peace plan put to Kyiv this week, with terms critics say constitute a Ukrainian capitulation.

A U.S. delegation that includes Army Secretary Daniel P. Driscoll, Secretary of State Marco Rubio and envoy Steve Witkoff will meet with Ukrainian officials in Geneva, a top U.S. official told ABC News Saturday.

Ukrainian President Volodymyr Zelenskyy said in a post to social media on Sunday that his advisers would also be meeting with French, German and British representatives in the Swiss city.

A U.S. official told ABC News that there are plans for the U.S. delegation to hold a separate meeting with a Russian delegation. No details were provided about the location of the planned meeting with the Russians.

In his social media post, Zelenskyy urged foreign partners to further strengthen Ukraine’s air defenses, as long-range nightly Russian strikes continue. On Saturday night into Sunday morning, Russia launched 98 drones into Ukraine, according to the Ukrainian air force. Sixty-nine of the craft were shot down or suppressed.

“In parallel with the diplomatic track, we must do everything to strengthen our defense against such wicked Russian attacks,” Zelenskyy wrote. “It is extremely important to speed up the implementation of all our agreements with partners regarding air defense systems and missiles for them.”

The U.S.-proposed 28-point peace plan was drafted in coordination with the Kremlin and with input from Rustem Umerov, the secretary of Ukraine’s National Security and Defence Council.

The plan includes a number of maximalist demands that the Kremlin has long demanded and that have been previously dismissed as non-starters for Kyiv, including that Ukraine cut its armed forces by more than half and cede swaths of territory not yet occupied by Russia.

Ukraine would also be forbidden from possessing long-range weapons, while Moscow would retain virtually all the territory it has occupied — and receive some form of recognition of its 2014 seizure of Crimea under the latest proposed U.S. plan.

Russian President Vladimir Putin said during a meeting of his Security Council on Friday that the Kremlin had received the proposal. “I believe that it could also form the basis for a final peace settlement, but this text has not been discussed with us in detail,” Putin said.

“I believe the reason is the same: the U.S. administration has not yet managed to secure the agreement of the Ukrainian side, as Ukraine is opposed to it,” Putin added. “Apparently, Ukraine and its European allies are still under the illusion that they can inflict a strategic defeat on Russia on the battlefield.”

In an address to the nation on Friday, Zelenskyy said Ukraine is facing “one of the most difficult moments in our history” and that Ukraine in the coming days may have to choose between “dignity” or the “risk of losing a key partner,” meaning the U.S.

He promised to “work calmly” and quickly with the U.S. on the plan and to search for “constructive solutions.” He added, “I will present arguments, I will persuade, I will offer alternatives.”

U.S. President Donald Trump suggested on Saturday that there is room for further negotiation. Asked by reporters whether this was his last offer, Trump replied, “No.”

“We’d like to get to peace,” Trump said. “One way or another we’ll get it ended.”

On Saturday, a bipartisan group of senators said they were told by Rubio in a phone call that the 28-point plan was developed by Russia, not the U.S.

In a statement on social media Saturday evening, Rubio denied the senators’ claims, asserting “the peace proposal was authored by the U.S.”

Rubio did not directly respond to the senators’ characterization of his message to them.

Rubio described the proposal as “a strong framework for ongoing negotiations,” adding, “It is based on input from the Russian side. But it is also based on previous and ongoing input from Ukraine.”