European Commission president, Ursula von der Leyen, tweets her response

Very concerned about announcements from the British government on its intentions to breach the Withdrawal Agreement. This would break international law and undermines trust. Pacta sunt servanda = the foundation of prosperous future relations.

It will be interesting to see how much further the EU is going to push this now that the UK has laid out their stance. Barnier's negotiating team is in London right now and their mandate is predicated on the withdrawal agreement. If that is undermined, then potentially the basis for any talks this week is essentially void so..