One of the European Union negotiators working on a post-Brexit trade deal with the UK has tested positive for coronavirus, leading to a suspension in the talks.
The two sides have been meeting in Brussels with time running out to reach a deal before the Brexit transition arrangements expire at the end of the year.
The EU's chief negotiator Michel Barnier said a member of his team tested positive.
???????? update: one of the negotiators in my team has tested positive for COVID-19. With @DavidGHFrost 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.— Michel Barnier (@MichelBarnier) November 19, 2020
Mr Barnier and his UK counterpart David Frost have been taking part in an intensified negotiating process in an effort to reach a deal which can be ratified by the end of the year, and any further delays could complicate matters.
Mr Barnier said that, together with Mr Frost, "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," he added.
Mr Frost said he was in "close contact" with Mr Barnier about the situation.
"The health of our teams comes first," he said and thanked the European Commission for their help and support.
UK officials in Brussels are working with the EU to discuss what will happen next.
It was unclear whether members of the negotiating team will have to self-isolate.
Earlier, two well-placed sources said the EU would not end the Brexit negotiations soon but instead would pursue what has been described as a "patient" approach.
Both sides are still said to be far apart on the so-called level playing field, fisheries and governance.
The apparent shift in strategy comes amid a determination by the EU that it will be in a better position to withstand a No Deal outcome than the UK.
The question of timing has loomed large in recent days as the EU confronts the difficulty of granting the European Parliament enough time to process any agreement before ratifying it during its plenary session, starting on 14 December.
It has always been assumed that the parliament would need at least four weeks to prepare for ratification, and that the UK was under less time pressure because its parliamentary procedures to ratify any agreement were more flexible.
However, it is understood the EU will seek legal ways to overcome any difficulties faced by either the European Parliament or member states in concluding formal ratification procedures, so as to avoid time becoming a source of pressure on Mr Barnier as the talks enter the critical final phase.
EU Trade Commissioner Valdis Dombrovskis said: "We actually have seen many deadlines come and go. But there is one deadline which will not be able to move, which is January 1st, the next year when the transition period ends."
Officials have said that the idea of provisionally applying parts of an agreement on 1 January is now being looked at, although one source said this would only provide a few weeks of extra negotiating time.
The UK would also have to agree to the provisional application of any agreement. It is understood that the issue has not "formally" entered the negotiations thus far.
It would also potentially only apply to certain elements of the future relationship. It is understood that a mechanism to allow both sides to resolve disputes in the future would not, for example, form part of any provisional application of the treaty.
Two sources have said the EU would not be the side to pull the plug by declaring that the talks had run their course.
"I don't see the EU walking away," says one official familiar with the negotiations. "There is zero political advantage for them to do that."
Another source said: "The timing on both sides is an issue but we are not going to be the ones to pull the plug and say we're not moving forward anymore.
"The pressure is more on the UK. At the end of the day, we still have the single market, we still have the Withdrawal Agreement."
EU leaders were due to hold a video conference this afternoon on the Covid pandemic. Brexit was not on the agenda, although a number of leaders were expected to raise the question of No Deal contingency planning.
However, the European Commission believes that a large amount of contingency planning was carried out last year in advance of two potential No Deal deadlines in March and October.
As such, it is understood that any fresh emergency No Deal contingency measures would be limited.
Michel Barnier is due to update EU ambassadors on the negotiations tomorrow. However, he is not expected to announce any major breakthrough in the negotiations, which have been in a more intensive phase for the past two weeks.
Additional reporting Tony Connelly