The European Council President has branded Foreign Secretary Jeremy Hunt’s comparison of the EU and Soviet Union as an unwise insult.
Donald Tusk demanded greater respect from the UK government, saying "unacceptable comments" were achieving nothing other than to raise the temperature of the Brexit negotiations.
Mr Tusk also rejected any suggestion the EU had not respected the dignity of the UK at the recent meeting of European leaders at Salzburg.
The European Council president - a former prime minister of Poland who was imprisoned as a young man living behind the Iron Curtain - made a clear reference to Mr Hunt’s controversial remarks after meeting with Irish premier Leo Varadkar in Brussels.
The European President said: "In respecting our partners, we expect the same in return."
"Comparing the EU to the Soviet Union is as unwise as it is insulting.
"The Soviet Union was about prisons and gulags, borders and walls, violence against citizens and neighbours.
"The European Union is about freedom and human rights, prosperity and peace, life without fear, it is about democracy and pluralism - a continent without internal borders and walls.
"As the President of the European Council and someone who spent half his life in the Soviet bloc, I know what I am talking about."
The EU council president added: "Unacceptable remarks that raise the temperature will achieve nothing except wasting more time."
Asked if Mr Hunt should resign over his comments at the Conservative Party conference, Mr Tusk replied: "That’s not my problem".
The key EU figure did however suggest the Tory conference had served as a distraction to the negotiations.
"I was party leader myself for 15 years and I know what the rules of party politics are," he said.
"But now the Tory party conference is over we should get down to business."
In an apparent reference to claims Prime Minister Theresa May and her Chequers plan for a future trade deal were not shown sufficient respect in Salzburg, Mr Tusk added:
"Telling the truth, even if difficult and unpleasant, is the best way of showing respect for partners, that’s how it was in Salzburg and that’s also how it will work in the coming days."
He added: "Emotional arguments that stress the issue of dignity sound attractive but they do not facilitate agreement.
"Let us remember that every actor in this process has their dignity and confrontation in this field will not lead to anything good."
Mr Tusk also referenced the less comprehensive Canada-style trading deal as advocated by Brexiteers like Boris Johnson and David Davis.
He said the EU was offering a "Canada plus, plus, plus deal", stressing the European desire for as close a relationship as possible with the UK after Brexit.
Mrs May has insisted her Chequers blueprint is the only proposal that would honour the referendum vote to leave the EU while avoiding the return of a hard border between Northern Ireland and the Republic.
Mr Tusk’s meeting with Mr Varadkar focused on the ongoing impasse over the Irish border and how free flowing frontier can be achieved if the UK adopts different customs and regulatory systems.
The European Council president said the EU remained "united behind Ireland" and the need to "preserve the Northern Ireland peace process".
"Despite the UK government’s rejection of the original EU backstop proposal we will not give up seeking a workable solution that fully respects the Good Friday Agreement as well as the integrity of the single market and customs union," he said.
Mr Varadkar thanked the EU for its “ongoing solidarity” with Ireland.
He said Ireland’s objectives remained as they have been since the start of the process - protecting the Common Travel Area on the island; ensuring no hard border; protecting the rights of Irish citizens living in Northern Ireland; and striking a trade deal with the UK.
"I want to very much agree with Donald Tusk in his call for us to get down to business,” he added.
"I am very keen to see an agreement concluded by November if at all possible – that is the interests of Ireland, the EU and the UK."