Face-to-face meetings between the chief negotiators in Brexit talks were suspended on Thursday after a member of the EU team tested positive for coronavirus, the bloc's Michel Barnier said.
A UK spokesman said the British and EU teams would continue to negotiate remotely "for the time being". This week's talks were in Brussels, but they were expected to resume in London next week.
"One of the negotiators in my team has tested positive for COVID-19," Barnier said in a tweet, as lower level meetings continued in Brussels.
"We have decided to suspend the negotiations at our level for a short period. The teams will continue their work in full respect of guidelines," Barnier said.
Barnier's British opposite number David Frost thanked the European Commission and said the negotiators would coordinate to ensure the safety of their colleagues.
"The talks will resume in person when it is judged safe to do so. The health and welfare of our staff are our priority," a UK spokesman said.
"The negotiations have been conducted throughout in a way that is consistent with applicable social distancing laws and guidance."
Barnier's team is due to brief EU ambassadors on Friday on the developments in the talks -- or the lack thereof.
The ill-timed hiccup came as London and Brussels are inching towards a trade agreement ahead of a year-end deadline, though both sides warn that failure remains possible.
A post-Brexit transition phase ends December 31 and the UK and Europe will need a trade deal to govern ties -- or face economic chaos after Britain leaves the EU single market.
With a late October deadline already blown, a deal is needed soon to allow time for legal vetting and ratification by the European Parliament, whose last scheduled meeting of the year is on December 16.
The Covid case comes at the most sensitive juncture, when the most senior negotiators will need to forge compromises on the toughest issues that have been blocked since talks began eight months ago.
"The circle dealing with the negotiations in Brussels is getting smaller, and tighter. The two sides now really are now in what can be described as a 'tunnel'" said Mujtaba Rahman, managing director of the Eurasia Group risk consultancy.
There are nevertheless several dozen UK officials in Brussels for the latest round of talks. They are not expected to self-isolate and will return to London in the comings days ahead of the next face-to-face meetings.
Both Barnier and Frost have previously caught the coronavirus and emerged safely from isolation. jit-dc/arp/tgb