Zelensky dismissed the demand as a regional “ultimatum” reminiscent of Adolf Hitler.
Ukraine has said that under any peace deal Russia must withdraw its troops from internationally recognised territory of Ukraine, including the Crimean peninsula.
There have been no direct talks between the two sides since the first week of the war.
Russia has not been invited to the summit in Switzerland and Moscow's close ally China will also not attend.
But Switzerland said on Friday that at least 57 heads of state and government would attend.
The United States, Ukraine's most important financial and military backer, will be represented by Vice President Kamala Harris.