The discussion between Trump and Putin came during high-stakes talks in Washington between Trump, Zelensky and several European leaders that back Ukraine in its fighting against Russia’s invasion.

“Putin mentioned Moscow” during their call on Monday, one of the sources told AFP, adding that Zelensky had said “no” in response.

A diplomatic source close to the discussions said that European leaders had told Trump that Putin’s proposal “did not seem like a good idea.”

After the summit in the White House on Monday that included the German, French, Finnish, Italian and UK leaders, Trump said a next step to stopping the fighting, now in its fourth year, would be a face-to-face meeting between Putin and Zelensky.

The Ukrainian leader has said repeatedly in recent weeks that he is prepared to sit down with Putin to end the Russian invasion, which has cost tens of thousands of lives and displaced millions.

Putin told Trump during the call on Monday that he was open to the “idea” of direct talks with Ukraine, Kremlin aide Yuri Ushakov said, according to state media.

Russian foreign minister Sergei Lavrov said Tuesday that any meeting between the Russian and Ukrainian presidents would have to be prepared “very thoroughly.”

Switzerland, meanwhile, had said earlier that it would grant Putin immunity if he came to the country for talks on peace in Ukraine, despite the International Criminal Court’s arrest warrant.

Trump met with Putin last week in the northern US state of Alaska, ending a years-long Western policy of isolating Putin.

The US leader walked away from the meeting without any guarantees of peace from the Russian president.