Slovak Prime Minister Peter Pellegrini and chief EU negotiator for Brexit Michel Barnier said here on Tuesday that a solution to the Irish border issue is crucial for Brexit.

"The situation relating to Ireland and Northern Ireland remains to be a sensitive issue, because the EU 27 is interested in maintaining the single market and all the freedoms that apply to it," Prime Minister Pellegrini made the remarks a joint press conference with Barnier.

For his part, Barnier said that bargaining on Brexit is "very negative" and the deal won't bring any benefits to either side. He stressed the need for certainty regarding the back-up solution - backstop. This is, according to his words, necessary to ensure the integrity of the internal market as well as security in Ireland.

"It is in our interest to defend the interests of the citizens of Europe - our citizens, our businesses and the integrity of the internal market and the related four freedoms that are our greatest wealth," added Barnier.

The agreement on the departure of the United Kingdom from the European Union is still not completely prepared, lacking, among other things, a solution to the border issue between Ireland and Northern Ireland.

Both London and Brussels want to avoid the introduction of checks at the future external border of the European Union between its member state and Northern Ireland, fearing a renewed tension in this UK province, however, they haven't agreed so far on the way how to do it.