In his late-night address to Ukrainians on Saturday, Mr Zelensky said that Russian aggression “was not intended to be limited to Ukraine alone” and the “entire European project is a target for Russia”.
“That is why it is not just the moral duty of all democracies, all the forces of Europe, to support Ukraine’s desire for peace,” he said.
“This is, in fact, a strategy of defence for every civilised state.”
His address came as civilians continued to flee eastern parts of the country before an expected onslaught and firefighters searched for survivors in a northern town no longer occupied by Russian forces.
Several European leaders have made efforts to show solidarity with the battle-scarred nation.
Mr Zelensky thanked the leaders of Britain and Austria for their visits Saturday to Kyiv, Ukraine’s capital, and pledges of further support.
He also thanked the European Commission president and Canada’s prime minister for a global fundraising event that brought in more than 10 billion euros for Ukrainians who have fled their homes.
Mr Zelensky repeated his call for a complete embargo on Russian oil and gas, which he called the sources of Russia’s “self-confidence and impunity”.
“Freedom does not have time to wait,” Mr Zelensky said. “When tyranny begins its aggression against everything that keeps the peace in Europe, action must be taken immediately.”
More than six weeks after the invasion began, Russia has pulled its troops from the northern part of the country, around Kyiv, and refocused on the Donbas region in the east.
Newly released Maxar Technologies satellite imagery collected on Friday showed an eight-mile convoy of military vehicles headed south to the Donbas region through the Ukrainian town of Velykyi Burluk.
Western military analysts said an arc of territory in eastern Ukraine was under Russian control, from Kharkiv — Ukraine’s second-largest city — in the north to Kherson in the south.
But counterattacks are threatening Russian control of Kherson, according to the Western assessments, and Ukrainian forces are repelling Russian assaults elsewhere in the Donbas, a largely Russian-speaking and industrial region.
Civilians were evacuating eastern Ukraine following a missile strike on Friday that killed at least 52 people and wounded more than 100 at a train station.
Ukrainian authorities have called on civilians to get out ahead of an imminent, stepped-up offensive by Russian forces in the east.
With trains not running out of Kramatorsk on Saturday, panicked residents boarded buses or looked for other ways to leave, fearing the kind of unrelenting assaults and occupations by Russian invaders that brought food shortages, demolished buildings and death to other cities.
“It was terrifying. The horror, the horror,” one resident told British broadcaster Sky, recalling Friday’s attack on the train station.
“Heaven forbid, to live through this again. No, I don’t want to.”
Ukraine’s state railway company said residents of Kramatorsk and other parts of the Donbas could flee through other train stations. Deputy Prime Minister Iryna Vereshchuk said 10 evacuation corridors were planned for Saturday.