No spirit of revenge in Brexit negotiations: Michel Barner

He rejected DUP criticism of his handling of the talks but said only a Northern Ireland-specific solution to the border question will work.

The EU's chief negotiator has visited the frontier three times and was acclaimed as a friend of Ireland by the Irish Government during a conference just a handful of miles south of the dividing line.

He said: "There is no spirit of revenge.

"I personally regret Brexit for many reasons and I am never aggressive.

"My door is open."

Northern Ireland and the Republic will share the UK's only land border with an EU state after Brexit and most of the operational details on how it will be handled are yet to be agreed between Britain and Europe.

Businesses fear checks on goods and people would disrupt free-flowing cross-border trade, and some critics believe it could even threaten the peace process.

Mr Barnier is holding a two-day visit to both sides of the border and addressed a conference in Dundalk in Co Louth on Monday.

He said: "Only Northern Ireland-specific solutions will work, only this can address the challenges created by Brexit in full."

He echoed Irish Taoiseach Leo Varadkar's call for real and meaningful progress by the June meeting of European leaders, but admitted it was an extraordinary and complex talks process.

Mr Barnier asserted there must not be a hard border on the island of Ireland and there was no choice but to protect the 1998 Good Friday Agreement which largely ended violence in Northern Ireland.

If a withdrawal agreement was to be found in October the framework of this agreement must be clear, the senior European representative warned.

Mr Barnier said a European Council meeting of leaders in June was a "stepping stone" to the final October summit when a Brexit deal must be sealed.

In response to criticism from pro-Brexit DUP leader Arlene Foster, Mr Barnier said his negotiating style was not aggressive.