Tánaiste and Minister for Foreign Affairs Simon Coveney has said that if the UK does not begin implementing the Irish Protocol it could "significantly damage" the prospects for even the most basic free trade agreement with the EU by the end of the year.
He was commenting on weekend reports that London was seeking ways to avoid putting in place checks and controls on goods moving from Britain to Northern Ireland when the transition period runs out at the end of this year.
The Protocol on Northern Ireland was agreed between the EU and UK as part of the Withdrawal Agreement.
Speaking to reporters in Brussels, Mr Coveney said: "The implementation of agreements that have already been struck are the test of good faith and trust. Without good faith and trust, building a good faith relationship is not going to be easy.
"If there isn't progress on the infrastructure needed to implement the Irish Protocol as part of the Withdrawal Agreement in the next few months, then I think that is going to be a very worrying signal for whether or not it's going to be possible to conclude something sensible before the end of the year.
"Michel Barnier and the Irish Government are at one on this. The WA involves significant commitments in the context of NI through the Irish Protocol that both the EU and the UK need to follow through on.
"If that isn't followed through on then I think it will damage significantly the prospects of being able to get even a bare bones trade agreement, along with a number of other things that need to be done, in place by the end of the year."
Mr Coveney was speaking ahead of a meeting of EU Foreign and European Affairs ministers, which was expected to formally adopt the EU's negotiating mandate so that the trade talks can begin early next week.
The Tánaiste added: "Whatever has been agreed in an international treaty needs to be agreed in full.
"The committees that are going to be set up in the context of the Irish Protocol are not committees that are set up to negotiate, they're committees that are set up to implement what has already been negotiated and agreed."
Earlier, German European Affairs Minister Michael Roth told reporters: "My message is crystal clear to our friends in London. Keep your promises based on the protocol."
🇪🇺🇮🇪 Ahead of the Council today, good to touch base with @simoncoveney, @HMcEntee and team. We will keep a very close eye on the implementation of the Withdrawal Agreement - this will be key for building a solid future partnership with the #UK. pic.twitter.com/8zqaLbYHWI— Michel Barnier (@MichelBarnier) February 25, 2020