“We knew that Putin was a bad man, we’ve known that for a long time now,” the top government official told RTE Radio One.
Mr Varadkar said: “But we didn’t think that he would be the Hitler of the 21st century, and I think he’s putting himself into that space.”
Comparing the Putin’s regime military aggression to rise of the Nazis, he added: “The last time I can think of that happening in Europe is in the 1930s and I think we should see this conflict in that context.”
Mr Varadkar also backed the UK’s stance over the call to ban Russia from the international Swift payment network, after Ukrainian president called for much tougher action from the west.
The deputy premier acknowledged that it could have economic implications for Ireland – but said they needed to be accepted.
“I don’t think we’re in that space where we can be concerned about the economic impact on Ireland when a democratic country in the EU, is being invaded and the attempt is being made to overthrow a democratic government there,” said Mr Varadkar.
Boris Johnson urged leaders from fellow Nato countries to take “immediate action” to ban Russia from the global banking system SWIFT during his call on Friday, arguing the move would “inflict maximum pain” on Putin and his regime.
Several European countries – including Germany and Italy – fear that cutting Russia out of the SWIFT payment system could make international trade more difficult and hurt their economies.
British defence secretary Ben Wallace also compared Putin to Hitler on Friday, as he questioned whether the Russian president was in his “right mind”.
Warning that he may not stop at Ukraine, Mr Wallace said the Russian leader would be “mad to attack a Nato country, but he would only have to be slightly more mad than he has shown himself to be”.
Defending previous comments in which he said there was a “whiff of Munich” about the Ukraine crisis, Mr Wallace suggested Russia’s full-scale invasion had proved him right.
“In Munich in 1938, Adolf Hitler all along had a plan to invade parts of Europe,” he said. “All the diplomacy was about a straw man attempt by him to buy time. Putin has been set on this for many, many months and certainly over a year.”
Meanwhile, dozens of Ukrainians gathered outside the Irish parliament on Thursday to express their anger at the Russian assault on their country.
They were joined briefly by premier Micheal Martin, who stopped to talk to some of those who had gathered on Kildare Street.
Mr Martin told the demonstrators that Ireland would work within the EU to respond to the crisis and promised to “keep in touch” with the Ukrainian community in Ireland to offer any help required.
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