Britain and Ireland traded barbs on Twitter on Sunday after British Brexit negotiator David Frost restated his view that the EU must agree "significant change" to the Northern Ireland protocol that governs trade and border rules in the province.
The protocol was part of the Brexit settlement Prime Minister Boris Johnson negotiated with the EU, but London has repeatedly said it must be rewritten less than a year after taking force due to the barriers businesses face when importing British goods into Northern Ireland.
Ireland's foreign minister Simon Coveney on Twitter asked: "Real Q: Does UKG (UK Government) actually want an agreed way forward or a further breakdown in relations?"
That drew a rebuke from Frost: "I prefer not to do negotiations by twitter, but since simoncoveney has begun the process."
Frost dismissed Coveney's argument that he was making new demands, saying that Britain's concerns over the European Court of Justice's role in the process were set out three months earlier.
"The problem is that too few people seem to have listened," Frost said.
On Saturday, Frost had released extracts of a speech he is due to make this week again calling for change and signalling a desire to free the protocol from the oversight of European judges.
Responding to that, Ireland's Coveney said Britain had created a new "red line" barrier to progress that it knows the EU cannot move on.
The row comes at the start of an important week in the long running debate over how to manage the flow of goods between Britain, Northern Ireland and the EU.
The European Commission is expected to present new measures on Wednesday aimed at resolving post-Brexit trading issues, but has repeatedly stated it is not willing to renegotiate the protocol.
A day before that, Frost is due to give a speech to the diplomatic community in the Portuguese capital, Lisbon.
He will say endless negotiation is not an option and that London will need to act using the Article 16 safeguard mechanism if solutions cannot be agreed rapidly.
Article 16 allows either side to take unilateral action if the protocol is deemed to have a negative impact.