Trump announced last week he would meet Putin on Friday in Alaska to negotiate an end to the 3.5-year war, which began with Russia's full-scale invasion of its neighbour.
Ukraine and its European allies fear that Trump, keen to claim credit for making peace and also hoping to seal lucrative joint business deals with Moscow, could align with Putin to cut a deal that would be deeply disadvantageous to Kyiv.
Germany said it was convening a series of top-level video conferences on Wednesday to prepare for the summit including one between European leaders, Zelenskiy, Trump and US Vice President JD Vance.
It will be the first time Zelenskiy and Trump have spoken since the Alaska summit was announced.
European leaders and EU and NATO officials would coordinate their approach beforehand, a German government spokesperson said.
Zelenskiy said on Monday that concessions to Moscow would not persuade it to stop fighting in Ukraine and that there was a need to ramp up pressure on the Kremlin.
"Russia refuses to stop the killings, and therefore must not receive any rewards or benefits," Zelenskiy wrote on X.
Zelenskiy said Russia was preparing its troops for new offensives instead of getting ready to stop the war in Ukraine.
"He is certainly not getting ready for a ceasefire and war end," Zelenskiy said in a nightly address.
He added, without providing any specifics, that Russia was moving its troops for new operations on Ukrainian soil.
He later held separate phone calls with the leaders of India and Saudi Arabia, which both have cordial ties with Moscow, in order to bolster international support for Kyiv's position ahead of the Trump-Putin talks.
European Union foreign ministers were holding a video conference on Monday afternoon to discuss their support for Kyiv and the upcoming meeting.
British Prime Minister Keir Starmer's spokesperson said London supported Trump's efforts to end the war in Ukraine but believed Kyiv must be involved in any settlement on ending the fighting.
"We will never trust President Putin as far as you can throw him, but we will support Ukraine and President Trump and European nations as we enter these negotiations," Starmer's spokesperson told reporters.
"Any peace must be built with Ukraine, not imposed upon it, and we will not reward aggression or compromise sovereignty."
The Alaska meeting comes as Trump has hardened his stance towards Moscow, agreeing to allow additional US weapons to reach Ukraine and threatening tariffs against buyers of Russian oil.
Even so, the prospect of Trump hosting Putin, on US soil, in what will be the first meeting between leaders of the United States and Russia since 2021, has revived fears that he might agree to a deal that forces big concessions from Kyiv or weakens European security.
Trump has said any peace deal would involve "some swapping of territories to the betterment of both" Russia and Ukraine, prompting consternation in Kyiv and European capitals.
"Regarding territorial issues, the Russian position is framed as a territorial swap, but it appears as a rather one-sided swap," a European Commission official said on Sunday.
Russia occupies about a fifth of Ukrainian territory, while Ukraine holds barely any Russian territory.
European leaders have underscored their commitment to the idea that international borders cannot be changed by force, fearing any deal forced on Kyiv could create a dangerous precedent.
