Zelenskiy said it did not mean war with Russia was imminent and, in an address to parliament, he urged lawmakers to stay calm and united, not to sow panic and not to exploit a stand-off with Russia for political gain.
Although Russia has massed tens of thousands of troops near Ukraine's borders, Zelenskiy has repeatedly pushed back against warnings by the US and other NATO allies that Russia could attack Ukraine at any moment.
He was speaking on Tuesday as he prepared to host the prime ministers of Britain, Poland and the Netherlands - all of them NATO member states - as part of efforts to defuse tensions with Russia and shore up international support for Kyiv.
"This decree (was prepared) not because we will soon have a war ... but so that soon and in the future there will be peace in Ukraine," Zelenskiy said.
There are currently nearly 250,000 people in Ukraine's armed forces, which are vastly outnumbered and outgunned by Russia's.
"We must be united in domestic politics. You can be in opposition to the government, but you can't be in opposition to Ukraine," Zelenskiy said.
"You can despise ... the government, the president, but you can't despise your own people, sow panic in order to reap political gains, keep people in a state of alarm."
NATO member states have rallied round Ukraine in recent weeks, with the US, Britain and Poland among countries offering military aid and calling for tough sanctions on Moscow if Russia launches an attack.
Moscow has denied any plans to invade Ukraine but has demanded sweeping security guarantees from the West, including a promise that Kyiv can never join NATO
British Prime Minister Boris Johnson will promise to uphold Ukraine's sovereignty on his visit to Kyiv.
After Zelenskiy finished speaking, lawmakers gathered in the well of the chamber holding up flags of countries that have shown their support, including Britain and Canada.
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