BERLIN, Dec. 15 (Xinhua) -- Ukraine's lead negotiator expressed optimism on Monday following a new round of high-level talks with a U.S. delegation in Berlin, stating "real progress" had been made toward a potential peace agreement.

Ukrainian President Volodymyr Zelensky on Monday concluded lengthy talks with U.S. President Donald Trump's special envoy Steve Witkoff and Trump's son-in-law Jared Kushner in Berlin.

Zelensky held talks with Witkoff and Kushner for over five hours on Sunday and for about another two hours on Monday.

After Monday's talks with the U.S. side, top Ukrainian peace negotiator Rustem Umerov said on social media platform X that negotiations have been constructive and productive, with "real progress achieved."

"We hope we will reach an agreement that will bring us closer to peace by the end of the day," said Umerov, also Secretary of the National Security and Defense Council of Ukraine.

Umerov added that the American team led by Witkoff and Kushner is "working extremely constructively" to help Ukraine find a way to a peace agreement that lasts.

Witkoff said on Sunday evening on X that "representatives held in-depth discussions regarding the 20-point plan for peace, economic agendas, and more."

According to German newspaper Die Welt, U.S. negotiators are urging Ukraine to give up the Donbas region.

Zelensky said on Sunday that the U.S.-proposed plan to establish a "free economic zone" in parts of the eastern Donbas region is unfair, citing lack of clarity over governance.

After the talks, Zelensky met with German President Frank-Walter Steinmeier and Bundestag President Julia Kloeckner.

Zelensky said in a statement that he and Steinmeier discussed the development of a framework document for ending the conflict and the content of specific points. Both sides shared a position on the importance of ensuring Ukraine's sovereignty, territorial integrity, and the protection of its national interests, said the statement.

Zelensky also discussed mechanisms to use frozen Russian assets for the benefit of Ukraine with Kloeckner. He added that he appreciates Germany's leadership on this issue. Enditem