The scramble for a post-Brexit trade deal headed into a new week Sunday after talks were overshadowed by the coronavirus crisis and broke up with no breakthrough on fishing rights.
As Belgium, France and many of their EU neighbours closed rail and air links to Britain, which had warned it has discovered a new strain of the virus, debate dragged on in Brussels.
After EU negotiator and Michel Barnier and his UK counterpart David Frost met at EU headquarters, the former French minister tweeted: "In this crucial moment for the negotiations, we continue to work hard.
"The EU remains committed to a fair, reciprocal and balanced agreement. We respect the sovereignty of the UK. And we expect the same," he said.
And Barnier stressed that, while both sides would control their own laws and waters, "we should both be able to act when our interests are at stake" -- a reference to a mechanism that must be agreed to ensure future fair competition.
A senior UK government source said the talks were expected to continue on Monday but "remain difficult and significant differences remain.
"We continue to explore every route to a deal that is in line with the fundamental principles we brought into the negotiations," he said.
Time is running out for a trade deal, with Britain due to leave the EU single market in 11 days, but both sides of the intense negotiations in Brussels now expect the talks to run on for three or four days until Christmas.
Without a deal, Britain's participation in the European project ends at midnight on December 31 (11 pm UK time) with a new tariff barrier to sharpen the shock of unravelling a half-century of partnership.
A European diplomat told AFP that Brussels had made its best offer and it was down to British Prime Minister Boris Johnson -- distracted by the worsening coronavirus crisis at home -- to decide whether he wants a deal.
The diplomat said the talks "could well continue over Christmas, now the UK is still making up its mind whether it is willing to pay the price for unprecedented access to the internal market".
The tough talk came as the negotiators scramble to secure a pact before December 31.
A failure to find a deal would exacerbate the growing chaos at EU and UK borders, where a pre-deadline rush of freight trucks has already caused long tailbacks.
And on Sunday, EU countries began to suspend transport links to Britain over the Covid crisis, after Johnson said a fast-spreading new variant of the disease had hit southeast England.
Britain intends to assume control over its waters on January 1, but is ready to allow continued access to EU fishing fleets for a transitional period under new terms.
UK negotiator David Frost wants Britain to take back more than half the fish currently assigned under the EU quota system, under a three-year agreement.
The European side insists the UK cannot have tariff-free access to the EU single market as a whole unless it accepts getting back only a quarter of the fish quota -- and that the transitional period should last six years.
The issue is highly charged for both Britain and for EU members with northern fishing fleets, such as France, the Netherlands, Belgium and Denmark.
EU fishermen fear that losing any access to the rich UK fishing waters will threaten their livelihoods.
Last week, the European Parliament highlighted a deadline of midnight (2300 GMT) on Sunday to receive a deal for review if MEPs are to ratify it before the end of the year.
Their UK parliamentary counterparts are in recess, but can be recalled within 48 hours to do likewise.
But EU capitals have not acknowledged any deadline -- and officials say they could provisionally ratify the agreement to avoid the economic shock of a no-deal divorce.
The urgency of reaching a deal is seen in long lines of trucks at the freight rail link through the Channel tunnel as British companies frantically stockpile.