Speaking at a special all-island conference in Dundalk, Co Louth, Mr Barnier also told ministers, opposition leaders, and business figures from the North and the Republic that there should not be a hard border.
His comments come amid increased scepticism about Britain providing a comprehensive solution to the border dilemma and Brexit by June. Mr Barnier said that negotiations were “complex”, that there should not be a hard border and that the EU wanted to protect the Good Friday Agreement.
There was full support for Ireland’s position and concern about the possibility of a hard border, said the Brexit negotiator.
Taoiseach Leo Varadkar said that neither Ireland nor the EU were not attempting a “land grab”, as alleged by figures in Britain.
He said Ireland had no interest in changing the status of the North until people wanted that, in what was viewed as a reference to the border poll option.
Mr Varadkar said that there was unity about making progress on the border issue before the next EU summit in June.
The EU has warned there must be a proposal from the UK on the table at that point if an agreement is to be reached on a withdrawal agreement by October, as is hoped.
The Taoiseach said there was now a difficult juncture in the talks and at some stage in the coming weeks there would be another important decision point.
It was essential there was progress by June, he said.
Michel Barnier speaks to gathered reporters at @Inter_Trade offices in Newry. Calls Brexit negotiations 'complex and extraordinary' but reaffirms EU's commitment to 'no hard border' on island of Ireland. @newsoncool @newsondowntown pic.twitter.com/eiBaHKdoXh— Damien Edgar (@damien_edgar7) April 30, 2018
However, asked whether there was a possibility of a chaotic Brexit, Mr Barnier admitted that there must be a clear framework for a solution for Ireland.
Until this was reached, there was a risk, a “real risk” of a disorderly Brexit, the audience was told.
However, he also said he was not pessimistic or optimistic and instead just “determined” to strike a deal on the Irish question.
“We need to agree rapidly by June on the scope of all-island customs and regulations, the safety and controls that we need to respect the single market,” said Mr Barnier.
He said the June meeting of European leaders in Brussels would be a “stepping stone” for the final summit in October, which is the deadline for reaching an agreement on withdrawal.
Fianna Fáil leader Micheál Martin told media at the conference at the Dundalk Institute of Technology that it needed to be established just how much progress needed to be made by June.
He also said that his party was concerned that the Irish question was being “pushed down the road” until October.
This was a major cause of concern, said Mr Martin, especially with the UK’s Brexit secretary David Davis in recent days saying he had no problem waiting until October before a solution on the border was found.
Sinn Féin leader Mary Lou McDonald accused Britain of trying to use Ireland as “leverage” during the Brexit talks, a move Ms McDonald deemed “cynical and reprehensible”.