He called on Kyiv's allies to apply greater pressure on Moscow to put the measure in place.
Zelenskiy, speaking at a joint news conference in Prague alongside Czech President Petr Pavel, said that unless increased pressure were applied, Russian leader Vladimir Putin would take no real steps to end the conflict.
"We believe that without increased pressure, Russia will not take real practical steps to end the war. Today marks the 54th day that Russia has ignored even the American proposal to completely cease fire," Zelenskiy told reporters.
"We believe that a ceasefire is possible at any moment, even starting today, and should last at least 30 days to give diplomacy a real chance."
Putin last week declared a three-day ceasefire over May 8-10 to mark the 80th anniversary of the victory of the Soviet Union and its allies over Nazi Germany in the Second World War.
Zelenskiy said such a measure is pointless and has called instead for an unconditional ceasefire for at least 30 days in line with a US proposal launched in March.
The Czech government has been a strong backer of Kyiv since Russia invaded Ukraine in 2022, and has led an initiative to supply Ukraine with large-calibre ammunition.
The Ukrainian president said that rather than putting tanks on display at a May 9 victory parade, Putin should be thinking "about how to actually end his war".
"Three things are needed. More sanctions against Russia, continued support for Ukraine, and a significant increase in defence cooperation across Europe," he said.
"Russia must know that Europeans will defend themselves."
Moscow has said it wants an unambiguous reply from Zelenskiy to its three-day offer.
Pavel said Russia had yet to show any indication it wanted to proceed with measures to end the war.
"If someone has all the cards in their hand to end the war, then it is President Putin, who can do it with a single decision," he told reporters.
"But so far, the will has not appeared."
Under the military initiative, the Czechs have used their diplomatic, business and industrial expertise to find large-calibre ammunition around the world and ship it to Ukraine with funding from NATO allies.
Pavel said in February that Ukraine had received 1.6 million rounds of large-calibre ammunition in the past year.
Zelenskiy said Ukraine hoped to receive 1.8 million shells under the program initiative in 2025
In an earlier social media post, Zelenskiy praised the initiative as "effective" and said cooperation would also be pursued in military aviation, expanding pilot training programs, and supporting Ukraine's fleet of F-16 aircraft.
Zelenskiy, who is accompanied on the trip by first lady Olena Zelenska, meets Czech Prime Minister Petr Fiala on Monday, with the Czech ammunition drive among the topics on the agenda.
The Ukrainian leader said on X social media site on Saturday he was preparing for upcoming foreign policy meetings focusing on helping push Russia into a ceasefire.
He also said he discussed air defence systems and sanctions on Russia with US President Donald Trump on the sidelines of Pope Francis' funeral at the Vatican on April 26.
The two agreed that a 30-day ceasefire was the correct first step towards ending the war.
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