Ukraine has "broken the backbone" of the Russian army, Zelenskiy said in a television interview.Â
"They will not be able to get back on their feet for the next few years."
His comments came after the last 2400 fighters of Mariupol surrendered and were taken captive.
Ukraine will take it all back, he said, adding that the country's forces will return the front lines to where they were before February 24, when Russia invaded.
"It will mean that they did not conquer us and that we defended our country," he said, though he noted this would be very difficult and that diplomacy would follow.
Meanwhile, Luhansk regional governor Serhiy Gaidai said in a social media post early on Saturday that Russia was trying to destroy the city of Sievierodonetsk, in Ukraine's east, with fighting taking place on the outskirts of the city.
"Shelling continues from morning to the evening and also throughout the night," Gaidai said in a video post on the Telegram messaging app.
Despite losing ground elsewhere in recent weeks, Russian forces have advanced on the Luhansk front.
Sievierodonetsk and its twin Lysychansk across the Siverskiy Donets River form the eastern part of a Ukrainian-held pocket that Russia has been trying to overrun since mid-April.
Russia's state gas company, Gazprom, said it had halted gas exports to Finland after it refused to agree to Russian demands to pay for Russian gas in roubles.
Finland and Sweden applied this week to join the NATO military alliance, a decision spurred by the Ukraine war.
Finnish state-owned gas wholesaler Gasum, the Finnish government and individual gas consuming companies in Finland have said they were prepared for a shutdown of Russian flows and that the country will manage without.
Most European supply contracts are denominated in euros or US dollars and Russia cut off gas to Bulgaria and Poland last month after they refused to comply with the new payment terms.
Portuguese Prime Minister Antonio Costa became the latest foreign leader to visit Kyiv and Ukraine's Prime Minister Denys Shmyhal said that he had signed an agreement for unspecified financial support.
with reporting from Reuters
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