The UK is "very close" to securing a Brexit deal on the Irish border and an agreement is expected within hours, an Irish official has said.
The official told an event in Brussels that border talks were "moving quite quickly", adding that Dublin was "going to work over the next couple of hours with the UK government to close this off".
European Commission president Jean-Claude Juncker has spoken over the phone with Theresa May and Irish PM Leo Varadkar and progress is said to have been made.
"Talks are continuing throughout the night," commission spokesperson Margaritis Schinas tweeted. "Early morning meeting possible with press/point thereafter. Tonight more than ever, stay tuned."
Meanwhile, a No 10 spokesperson said were talks were "ongoing".
It comes as European Council president Donald Tusk has scheduled a Brexit-related press briefing at 6.50am GMT on Friday morning.
The EU has given Theresa May three days to solve the Irish border deadlock and other initial divorce issues, otherwise Brexit negotiations will not move on to trade talks before the end of the year.
The Prime Minister looked set to reach an agreement in Brussels on Monday, only to see DUP leader Arlene Foster withdraw her support over fears of regulatory alignment between Northern Ireland and the Republic after Brexit.
Brexit negotiators in Brussels, Dublin and London are working on a revised text of that near-deal, according to Irish MEP Brian Hayes.
"It's not that the text is changed in substance from the original but that it might be modified somewhat, new language, but as we speak those negotiations are continuing and have intensified," the Fine Gael politician told RTE.
Mrs May spoke with both Mrs Foster and Mr Varadkar on Wednesday in her attempt to salvage a deal with the EU.
After his call with the Prime Minister, Mr Varadkar said Mrs May was hoping to return with a new formal written offer "tonight and tomorrow".
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Meanwhile, Dutch Prime Minister Mark Rutte warned that EU member states would not "loosen" their position on the "fundamental" points of citizens' rights, the so-called "divorce bill" and the Irish border.
Despite the difficulties facing the Prime Minister ahead of Brussels' looming deadline, Transport Secretary Chris Grayling insisted he was "very optimistic" about the hopes of a Brexit agreement.
Speaking to Sky News, the Cabinet minister played down suggestions Mrs May should walk away from negotiations if talks did not progress.
He said: "Nobody should expect us to sign up to a bad deal for Britain, but I'm very optimistic about this.
"I think we want an agreement. All my conversations with other European ministers suggests they want an agreement. I'm sure we'll get there."
Answering questions after a speech on Thursday, Foreign Secretary Boris Johnson said it was time for Britain and the EU to "get going" on the second phase of talks.
He said: "That's the exciting bit. That's the bit where we will achieve a new trading relationship with our friends and partners.
"We can get it done, we just need to get on with it, and I hope very much that the December European Council will mark that progress."