Lucerne, Switzerland - US President Joe Biden's absence from a Ukraine peace summit in Switzerland would be akin to giving Russian leader Vladimir Putin a standing ovation, Ukrainian President Volodymyr Zelensky said on Tuesday, urging maximum participation.

Biden has yet to confirm whether or not he will attend the conference, set for mid-June.

"If he is not present, it will be just like applauding Putin: personally applauding and doing so standing," Zelensky said during a visit to Brussels.

"I believe that the Peace Summit needs President Biden, and other leaders who are looking at the US response also need him," he added.

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Zelensky has said dozens of world leaders will attend the summit. He claimed Tuesday that attending or not is a "choice" between wanting peace or war in Ukraine.

"If you want peace, you will be there and you will speak, even if you don't agree with something," he said.

"And if you want war, you will go to the mob that Russia wants to organize," he added, saying that countries who will skip the summit are "satisfied with war."

Zelensky has ruled out Moscow's participation and accused Putin of trying to derail the summit.

"Putin is very scared of the peace summit," he said. "He has been trying to thwart this summit and continues to do so."

He said the Kremlin is "doing everything" for the "further expansion of the war."

Russia has made gains in eastern Ukraine in recent weeks, launching a renewed ground offensive in the northeast of the country.

The summit will take place almost 28 months into Moscow's invasion.