Britain and the EU were seen to be closing in on a detailed draft Brexit deal on Tuesday, although officials voiced scepticism it would be ready in time for a key European summit this week.
The pound jumped to its highest level in five months on cautious optimism voiced by both sides that an outline agreement could soon be struck.
However Irish Prime Minister Leo Varadkar, speaking in a Dublin media conference, warned that "the gap was still quite wide, particularly on the issue of customs" along the Irish border with Northern Ireland.
An EU official told AFP late Tuesday: "Talks are ongoing. I have no update right now." EU negotiator Michel Barnier said a text must be on the table by early Wednesday if it is to be put before leaders at the two-day EU summit starting Thursday. A special sitting of the British parliament is scheduled for Saturday.
If the early-Wednesday deadline is missed, officials said talks could always resume next week and a special summit be called just in time for Prime Minister Boris Johnson to fulfil his pledge to lead Britain out of the bloc on October 31.
One European source told AFP that it was "possible" a preliminary legal text could be reached perhaps by late Tuesday. But another was unable to confirm any breakthrough.
Varadkar said: "Whether we'll be able to conclude a revised withdrawal agreement, which after all is an international treaty, in time for the summit on Thursday, that's as of now unclear."
"One thing is clear, Britain will develop into another competitor on the doorstep of Europe," she told industrialists. "And therefore the EU will be challenged to become more competitive and to assume geopolitical responsibility."