The EU's chief Brexit negotiator has described as "totally unacceptable" a reported offer from the UK on the fisheries element of the future relationship negotiations.
Michel Barnier told EU ambassadors in Brussels that the EU was ready to pursue a post-Brexit trade deal to the end of the year "or beyond".
One diplomat told RTÉ News that a deal may not be ready in time for the 31 December deadline.
The AFP news agency, quoting sources, said Mr Barnier could not guarantee that there would be a deal, but that "our door will remain open until the end of the year and beyond, as well".
Mr Barnier told ambassadors the UK proposal that the EU transfer 35% of the value of fish caught by EU boats in UK waters to the British fleet did not include pelagic stocks, and that if it did the UK offer would be closer to 60%.
He told ambassadors that the EU’s offer of 25% of the value of fish caught in UK waters was final.
"If you compare like with like it’s 60% versus 25%, that’s the real figure," said one EU official. "It’s not 35% versus 25%."
It is understood that Mr Barnier said the UK was also excluding any access for European boats to its six-mile to 12-mile fishing zone.
Earlier, Mr Barnier vowed to continue to push for a post-Brexit trade deal through the last ten days before Britain leaves the single market.
He told reporters: "We are really in the crucial moment, and we are giving it the final push.
"In ten days the UK will leave the single market and I will continue to work, in total transparency with the European Parliament and the member states."
Mr Barnier updated ambassadors from the 27 European Union nations this afternoon on the state of the negotiations with the UK. He will also brief MEPs later this evening.
Taoiseach Micheál Martin has said that he thinks a Brexit deal is likely.
During a media briefing this evening he told journalists that there has been a lot of progress made in the last two weeks, particularly in relation to the level playing field and the dispute resolution mechanism.
However, he said that it is fair to say that fisheries is proving to be "very, very difficult".
Mr Martin said that a number of member states are fighting to protect the sector.
However, the Taoiseach believes a deal is likely.
"The sense I would have is that given the progress that has been made, that I think a deal is more likely than less likely."
Mr Martin said he would like to see a deal done before Christmas, however, he said it could go beyond that.
Micheál Martin said that there are a range of issues around fishing that are not just centred on percentage share.
He told journalists that "there's a transition timeline, length of time for a transition period after the deal is done so there are a number of ways of dealing with the issue."
The UK leaves the single market and customs union on 31 December and will face tariffs and quotas on trade with the EU unless a deal is reached.
But talks in Brussels remain difficult, with "significant differences in key areas", including fishing rights and rules on maintaining fair competition.
Diplomat says a deal may not be ready in time for the Dec 31 deadline.— Tony Connelly (@tconnellyRTE) December 22, 2020
In a sign of the intensive diplomatic activity, British Prime Minister Boris Johnson is in "close contact" with European Commission president Ursula von der Leyen.
Sources said the pair were speaking "from time to time given there isn't long left" until the end of the Brexit transition period next week.
Mr Johnson has continued to insist the UK will "prosper mightily" without a deal, despite warning that it could add further damage to an economy already ravaged by coronavirus.
He spoke to Ms von der Leyen yesterday, according to Politico, although No 10 would not publicly confirm the call or what they discussed.
The two leaders reportedly spoke about fresh proposals on fishing rights.
Downing Street insiders flatly rejected reports that there has been a breakthrough in the row over quotas.
A Number 10 insider described the reported compromise as "b*******" and officials have warned that significant differences remain between the two sides.
At a press conference yesterday, Mr Johnson said the position is "unchanged" and insisted the UK will thrive without a deal, relying on World Trade Organisation terms.
Additional reporting AFP, PA