By Friederike Heine, Matthias Williams ‌and Olena Harmash

BERLIN/KYIV, Dec 14 (Reuters) - President Volodymyr Zelenskiy offered to drop Ukraine's aspirations to join the NATO military alliance as he held five hours of talks with U.S. envoys in Berlin ‍on Sunday to ‌end the war with Russia, with negotiations set to continue on Monday.

Trump's envoy Steve Witkoff said "a lot of progress was made" as he and Trump's son-in-law Jared Kushner met Zelenskiy in the ⁠latest push to end Europe's bloodiest conflict since World War Two, though full details were not divulged.

Zelenskiy's ‌adviser Dmytro Lytvyn said the president would comment on the talks on Monday once they were completed. Officials, Lytvyn said, were considering the draft documents.

"They went on for more than five hours and ended for today with an agreement to resume tomorrow morning," Lytvyn told reporters in a WhatsApp chat.

Ahead of the talks, Zelenskiy offered to drop Ukraine's goal to join NATO in exchange for Western security guarantees.

The move marks a major shift for Ukraine, which has fought to ⁠join NATO as a safeguard against Russian attacks and has such an aspiration included in its constitution. It also meets one of Russia's war aims, although Kyiv has so far held firm against ceding territory to Moscow. 

"Representatives held in-depth discussions regarding the 20-point plan ​for peace, economic agendas, and more. A lot of progress was made, and they will meet again tomorrow morning," Witkoff ‌said in a post on X.

The talks were hosted by German Chancellor Friedrich Merz, who ⁠a source said had made brief remarks before leaving the two sides to negotiate. Other European leaders are also due in Germany for talks on Monday.

"From the very beginning, Ukraine's desire was to join NATO, these are real security guarantees. Some partners from the U.S. and Europe did not support this direction," Zelenskiy said in answer to questions from reporters in a WhatsApp chat. 

"Thus, today, bilateral ​security guarantees between Ukraine and the U.S., Article 5-like guarantees for us from the U.S., and security guarantees from European colleagues, as well as other countries — Canada, Japan — are an opportunity to prevent another Russian invasion," Zelenskiy said.

"And it is already a compromise on our part," he said, adding the security guarantees should be legally binding.

Russian President Vladimir Putin has repeatedly demanded Ukraine officially renounce its NATO ambitions and withdraw troops from the about 10% of Donbas which Kyiv still controls. Moscow has also said Ukraine must be a neutral country and no NATO troops can be stationed in Ukraine.

Russian sources said earlier ​this year that Putin ‍wants a "written" pledge by major Western powers not to enlarge ​the U.S.-led NATO alliance eastwards - shorthand for formally ruling out membership to Ukraine, Georgia, Moldova and other former Soviet republics.

Sending Witkoff, who has led negotiations with Ukraine and Russia on a U.S. peace proposal, appeared to be a signal that Washington saw a chance of progress nearly four years after Russia's 2022 invasion. 

Under pressure from Trump to sign a peace deal that initially backed Moscow's demands, Zelenskiy accused Russia of dragging out the war through deadly bombings of cities and Ukraine's power and water supplies.

A ceasefire along the current front lines would be a fair option, he added. 

'CRITICAL MOMENT'

Germany's Defence Minister Boris Pistorius said it was a "good sign" Trump had sent his envoys while fielding questions in an interview with the ZDF broadcaster on the suitability of Witkoff and Kushner, two businessmen, as negotiators. 

"It's certainly anything but an ideal setup for such ⁠negotiations. That much is clear. But as they say, you can only dance with the people on the dance floor," Pistorius said.

On the issue of Ukraine's offer to give up its NATO aspirations in exchange for security guarantees, Pistorius said Ukraine had bitter prior experience of relying on security assurances. ​Kyiv had in 1994 agreed to give up its Soviet-era nuclear arsenal in exchange for territorial guarantees from the U.S., Russia and Britain. 

"Therefore, it remains to be seen to what extent this statement Zelenskiy has now made will actually hold true, and what preconditions must be met," Pistorius said. 

"This concerns territorial issues, commitments from Russia and others," he said, adding mere security guarantees, especially without significant U.S. involvement, "wouldn't be worth much."

Britain, France and Germany have been working to refine the U.S. proposals, which in a draft disclosed last month called for Kyiv to cede ‌more territory, abandon its NATO ambitions and accept limits on its armed forces.

European allies have described this as a "critical moment" that could shape Ukraine's future, and sought to shore up Kyiv's finances by leveraging frozen Russian central bank assets to fund Kyiv's military and civilian budget.

(Reporting by Friederike Heine, Matthias Williams, Olena Harmash, Andreas Rinke, Ron Popeski, David Ljunggren; writing by Matthias Williams; editing by Alexander Smith and Chris Reese)