Dec. 29 (UPI) -- Ukrainian President Volodymyr Zelensky said Monday that he asked U.S. President Donald Trump to extend America's security guarantee against future Russian aggression by an additional 35 years during key peace negotiations at Mar-a-Lago.

Zelensky said the request was to increase the duration of the guarantee to 50 years from the 15 years in the current 20-point-plan under discussion at Sunday's two-and-a-half-hour-long talks, which senior European leaders joined remotely.

In an upbeat news conference afterward, both men hailed what they said was the great progress that had been made but with a slight gap in their assessment, with Trump saying they were "close to 95%" agreed on the issue, whereas Zelensky said it was "100% agreed."

Neither Zelensky nor Trump referenced specific durations of time regarding guarantees, but Trump stressed that he expected European countries to step up and "take over a big part" of the responsibility for the guarantees -- with U.S. support.

However, the pair conceded other "thorny issues" remained, principally land, including the question of Ukraine's Donbas region, with an ongoing gap between the Russians who want Ukraine to hand it over -- including areas it still controls -- and Ukraine, which has ruled it out.