European Council President Donald Tusk said that former London mayor Boris Johnson had "crossed a boundary" when he compared the EU to Adolf Hitler in comments made earlier this week.Johnson, who is one of the main proponents of Britain leaving the EU, said in an interview to the Telegraph on Sunday that the ambitions of the European Union to create a superstate by unifying the entire continent under one government body is comparable to Hitler's attempt to conquer Europe. Tusk told reporters in Copenhagen, "When I hear the EU being compared to the plans and projects of Adolf Hitler I cannot remain silent." The European Council president said that "such absurd arguments should be confidently ignored if they hadn’t been formulated by one of the most influential politicians in the [UK’s] ruling party. Johnson is the main voice in the "out" camp ahead of the June 23 referendum in which British citizens are set to vote on whether or not to remain in the EU . The Brexit campaign took a three-point lead over the "Remain" campaign in a survey published by polling firm TNS on Tuesday. Two of three polls published on Monday put the "In" camp ahead."Napoleon, Hitler, various people tried this out, and it ends tragically," said Johnson in his interview with the Telegraph. "The EU is an attempt to do this by different methods," he added.“Boris Johnson crossed the boundaries of a rational discourse, demonstrating political amnesia," Tusk said. He acknowledged that Johnson was not the only person to hold such opinions.“In some sense, he illustrated a state of mind and emotions of many Europeans, not only from the UK. In no way, however, can this be an excuse for this dangerous blackout," he said.The European Council which Tusk has been president of since 2014, is the body that comprises the heads of state of EU member states. Tusk formerly served as the prime minister of Poland.Tusk said the EU was "a common tool, not a superstate," a means for states to cooperate rather than a government for Europe: "The EU may be blamed for many things, but it still remains the most effective firewall against the ever dangerous, and often tragic conflicts among the nations of Europe."The only alternative ... is political chaos, the return to national egoisms and in consequence the triumph of anti-democratic tendencies, which can lead to history repeating itself."A British exit from the EU, already shaken by differences over migration and the future of the euro zone, would rip away its second-largest economy, one of its top two military powers and by far its richest financial center.Reuters contributed to this report.