"Brexit is a choice made by the British people and a choice that was pushed by certain people who predicted easy solutions", Macron said, referring to the Britain's June 2016 Brexit referendum campaign.
Speaking Thursday in Salzburg, Donald Tusk, President of the European Council, said key aspects of Brexit proposals, agreed at her Chequers country retreat in July, "will not work" in their current form.
Mrs May attended a crucial meeting with her European counterparts in Salzburg this week during which she planned to promote her Brexit deal.
Asked about reports Mrs May is willing to concede to some regulatory checks at Irish Sea ports, Mr Varadkar said he didn't want to comment on details of proposals without anything in writing.
"Yesterday Donald Tusk said our proposals would undermine the single market".
European powerhouses ambushed the Prime Minister by outright condemning her proposals, particularly her vision for the Irish border. What we have here are faraway governments siding with Britain's own bruised and aloof political and cultural elites to put pressure on the British electorate to think again and vote again and get it "right" this time.
"But the EU is proposing to achieve this by effectively keeping Northern Ireland in the customs union". "So we now need to hear from the European Union what the real issues are and what their alternative is so that we can discuss them".
'That is not the way to command a exhausted group of leaders who are all bit sick of each other, ' one diplomat told The Times.
"That would make a mockery of the referendum we had two years ago".
By that time the leaders had already been through a scratchy four-hour debate on the migration crisis - a bigger concern than Brexit for many of them.
The situation was not helped by the emergence of a report that Trade Secretary Liam Fox was planning to slash food standards after Brexit to give the United Kingdom a competitive advantage and secure a USA trade deal.
Nigel Dodds, deputy leader of Mrs May's DUP minority government allies, said the events in Salzburg provide "more evidence of the unreasonable and inflexible approach of the EU" and said: "The UK Government must demonstrate a resolute determination not to be bullied".
Both London and Brussels say they want a divorce deal, though there is limited time if the British and European Union parliaments are to ratify a deal by March 29.
"I will not overturn the result of the referendum nor will I break up my country", she said.
With a defiant tone, May concluded by saying: "We need serious engagement on resolving the two big problems in the negotiations and we stand ready".