US president Donald Trump has reportedly agreed to a key Ukraine demand for postwar security guarantees ahead of Friday’s Alaska summit with Vladimir Putin.

Volodymyr Zelenskiy, the Ukrainian president, said Mr Trump’s promise left him optimistic that the summit, to which he is not invited, will bring progress in ending the three-and-a-half year conflict.

European leaders, including Mr Zelenskiy, held a video call with Mr Trump in a bid to influence his meeting with Mr Putin.

After the call, Mr Zelenskiy declined to answer directly if, as the price of peace, he would accept territorial losses.

“We want a ceasefire, we want strong security guarantees and president Trump confirmed this and said he supports this,” said Mr Zelenskiy during a surprise visit on Wednesday to Berlin. “Russia cannot have right of veto regarding our own perspective in Europe and Nato. What we need is to exert pressure to achieve peace.”

Regarding Mr Trump’s recent talk of “land swaps” between Russia and Ukraine, Mr Zelenskiy declined to rule out the idea. Instead, hesitating for a moment during a press conference, he added that “our territorial integrity is something that will be decided by the Ukrainians”.

German chancellor Friedrich Merz, who initiated Wednesday’s virtual gatherings, said subsequent talks with Mr Trump and vice-president JD Vance had been “extremely constructive and a good conversation” with “great unity” on the key issues.

Mr Merz told Mr Trump he could count on European leader’s “full support” for any deal that maintains European and Ukraine’s security interests and the inviolability of national borders.

“We made clear that Ukraine must be at the table as soon as follow-up meetings take place,” said Mr Merz at a joint press conference with his Ukrainian visitor. “We want negotiations to proceed in the right order, with a ceasefire at the outset.”

The German leader said US president “largely shared” the European wish to “increase the pressure” if Russia refused to make concessions and, as in the past, continued to talk with the West while continuing its military campaign.

“This cannot continue, otherwise these discussions are not credible,” said Mr Merz. “I am hoping that Mr Trump will try to be assertive here.”

Wednesday’s trip to Berlin marked the high point of a frantic week of diplomacy for Mr Zelenskiy.

In his first video conference, he joined Mr Merz and other leaders from the so-called “coalition of the willing”: heads of state and government of Britain, Finland, France, Italy, Poland and the European Union – as well as Nato secretary general Mark Rutte.

The former Dutch prime minister said last week that some Ukrainian territory might end up being de facto controlled by Russia, even if not formally recognised.

“The ball is now in Russia’s court,” said Mr Rutte after Wednesday’s meeting, praising Mr Trump’s “leadership and close co-ordination with allies”.

After the call, French president Emmanuel Macron said Mr Trump agreed to use his Alaska meeting with Mr Putin to push for a ceasefire before peace talks, a position Russia rejects.

Mr Macron insisted that, while there were “currently no serious territorial exchange schemes on the table”, Mr Trump agreed that “territories belonging to Ukraine cannot be negotiated and will only be negotiated by the Ukrainian president”.

Mr Zelenskiy confirmed in Berlin that all parties on Wednesday’s video call agreed his country must be involved in any territorial talks as part of a ceasefire agreement with Russia. Such guarantees from Washington – should they hold – will go some way to assuaging Ukraine’s fears, based on previous remarks by Mr Trump, that a carve-up of its territory could be part of a peace deal agreed between Washington and Moscow.

The Ukrainian leader played down talk of a “historic” encounter, echoing Mr Trump’s insistence that Alaska will be a “feel-out” meeting with the Russian leader. Mr Zelenskiy said he urged Mr Trump not to believe Mr Putin’s “bluffs” that Russia could occupy all of Ukraine, or that sanctions were ineffective.

He said the US president promised to call him after the meeting “to discuss results if there will be results, so we can discuss the next steps”.

Mr Merz declined to be drawn on how European allies would contribute to the security guarantees sought by Kyiv.

Its European allies would “continue to strengthen the Ukrainian army”, Mr Merz added, and their contributions, “differing from country to country, were not discussed” on Wednesday.

“We will discuss that when we find ourselves on a path to peace,” he added.