European Commissioners unanimously rejected UK Brexit proposals for the Northern Ireland border at a top-level meeting on Wednesday in Brussels.
Commissioner Günther Oettinger told reporters that "all colleagues agreed with Barnier" at the gathering of the Commission's cabinet, officially known as the College of Commissioners.
The firm rejection comes ahead of talks between chief negotiator Michel Barnier and his British counterpart on Thursday in the EU capital.
A spokesperson for the European Commission said in a statement after Wednesday's meeting that the "EU remains constructive even when British emotions run high" – an apparent reference to hostile briefings emanating from Downing Street earlier in the week.
Giving an account of the College of Commissioners meeting, Mr Oettinger told reporters: "Once again, we discussed the proposal from the British government, and basically, all colleagues agreed with Barnier: namely the proposal from the British government does not represent a satisfactory solution."
Mr Oettinger, a senior commissioner in charge of the EU's budget, also rejected suggestions that the bloc would offer the UK some kind of veto or time-limit to the Northern Irish backstop, as proposed by the UK.
Reports emerged on Wednesday evening that officials were discussing giving the Northern Ireland assembly some kind of veto over the plan – though not to the extent demanded by the British proposals.
"A backstop can only take effect if it is not subject to a time limit, that it wouldn't automatically end after two, three, or four years," the Commissioner said.
"But also, if it is not one that could be set aside by a third party. The regional government in Northern Ireland would be a third party.
"It wouldn't be possible to have this if they could end or start applying conditions to it. As far as we're concerned, in the withdrawal agreement, the text we have remains vital."
The rumoured proposals for a "double majority" veto that would had required the consent of both the republican and unionist communities were in any case rejected by both Sinn Fein and the DUP on Wednesday morning, leaving them dead in the water.
Other than the veto plans, the EU is concerned about the customs element of the UK proposals - which would see the reintroduction of checks on goods moving between Ireland and Northern Ireland.