The European Commission vice president Maros Sefcovic has said the UK implementing what it had agreed to in December was a pre-requisite for any further flexibilities the EU would consider on the Northern Ireland Protocol.
Speaking ahead of a meeting of the EU/UK Joint Committee, which oversees the implementation of the Protocol, Mr Sefcovic said Brexit had consequences and these were reflected in the Protocol and in the EU/UK free trade agreement, concluded on Christmas Eve.
Separately on 17 December, Mr Sefcovic and his fellow co-chair of the Joint Committee Michael Gove had concluded an agreement on implementing the Protocol, including two separate grace periods for food products entering Northern Ireland from Great Britain, and other facilitations.
However, Mr Sefcovic told a news conference in Brussels this evening that the UK had still not implemented elements of the December agreement, such as the ability of EU officials in Northern Ireland to have real time access to UK customs IT systems, and an alleged failure by UK officials to carry out physical checks on food consignments entering Northern Irish ports from GB.
In a strong signal that the EU will not agree to any major concessions during tomorrow's meeting, Mr Sefcovic warned: "Not everything can be solved. There are inevitable consequences of Brexit, and simply we have to follow EU law. We have to follow the agreement we just signed.
"We can do our utmost to minimise the disruption to the daily lives of citizens on the island of Ireland. The best response to make sure this disruption is minimised to the extent possible is full implementation of the Protocol."
EU and UK officials today held a virtual meeting of the so-called Specialised Committee, which prepares the groundwork for the more political Joint Committee meeting, which takes place tomorrow.
It is understood the EU side listed a number of complaints about the non-implementation of the December agreement, complaints which the UK side "robustly" contested.
RTÉ News understands that if the EU does agree to any extensions of the two grace periods, then it will be on the basis that they are a "bridge" to a permanent settled state on how the Protocol is operated.
"The EU is linking any consideration of further grace periods to implementation by the UK of its commitments," according to one diplomat briefed on the meeting, "and also making the strong point that if there were to be a further extension of grace periods it would have to be a bridge to the permanent settled state".
"We're not getting into a rolling period of extensions every six months or so."
It is also understood that the European Commission is exploring the idea of a bilateral veterinary agreement between the EU and UK that might alleviate some of the more acute problems facing trade moving from GB to Northern Ireland.
However, it is understood the UK turned down this idea during the free trade negotiations as it would have required a degree of alignment with EU food safety and animal health rules.