Writing on Telegram, Zelensky said Kyiv had received no official ceasefire proposal from Moscow but was acting unilaterally.
"We believe human life has incomparably greater value than the 'celebrations' of any anniversary. Therefore, we are announcing a silence regime starting from midnight on the night of May 5-6," he said.
Zelensky added that Ukraine would respond "symmetrically" from that point forward, and challenged Russia to take concrete steps toward ending the war.
"The time has come for Russian leaders to take concrete steps to end this war, since the Russian Defense Ministry acknowledges it cannot hold a parade in Moscow without Ukraine's consent," he said.
Earlier on Monday, the Reuters news agency reported that Russian President Vladimir Putin had ordered a two-day ceasefire for May 8-9, coinciding with Russia's Victory Day commemorations marking the Soviet defeat of Nazi Germany in World War II.
Zelensky had earlier dismissed a one-day pause as "dishonest."
The announcement follows a April 29 phone call between Putin and US President Donald Trump, in which Trump said he had suggested "a little ceasefire."
"I suggested a small ceasefire and I think he might do it," Trump told reporters.
The last ceasefire, declared for Orthodox Easter on April 11-12, lasted 32 hours on paper. Ukraine's General Staff reported Russian forces violated its terms 10,721 times.
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Source: PAP
Click on the audio player above for a report by Marcin Matuszewski.