The EU's chief negotiator Michel Barnier has denied claims he has been "aggressive" towards Northern Ireland unionists, saying his door was "always open".
Barnier hit back at claims by the leader of the Democratic Unionist Party (DUP) Arlene Foster that he was not an "honest broker", saying he was the "negotiator for the 27. Mrs Foster and some others have to understand that and respect that."
Barnier said that although he "regretted Brexit" there was "no spirit of revenge or punishment".
Foster's criticisms come in response to Barnier's suggestions back in February that the question over a border on the island of Ireland, which remains unresolved, could be solved by Northern Ireland remaining in the customs union after Brexit. The border issue has been cited as the chief hurdle to be overcome in the Brexit talks.
Foster made it clear she did not accept Barnier's solution. She told the BBC: "There are two jurisdictions on the island of Ireland, we are part of the United Kingdom, they have to respect the constitutional reality and in terms of that they have to understand that we want to remain part of the United kingdom not just from a constitutional or political point of view, but from an economic one as well."
Barnier has maintained that a "backstop" option for the Irish border must remain in place. The backstop was seen as hugely controversial because it would keep Northern Ireland in the customs union and Single Market – something which Theresa May said would never be acceptable.
However, in the transition agreement announced in March, it was back on the table as a last resort.
The Northern Ireland border question comes as the government continues to grapple with options surrounding the customs union.
The government was defeated for the seventh time in the House of Lords today, as it voted on the EU Withdrawal Bill. The amendment will allow parliament to alter the final Brexit settlement if the deal is rejected by MPs.
Originally ministers had said that if parliament rejects the Brexit deal agreed by the UK and EU negotiating teams it would cause the UK to fall out of Europe with no deal.
The amendment, which was passed by a majority of 91, was supported by 19 rebel Conservative peers.