UK Prime Minister Theresa May is in Brussels for last-ditch talks to hammer out a deal on the terms of Britain's exit from the EU.

Britain and the EU appear to be moving closer to a Brexit divorce deal, as diplomatic efforts between London, Brussels and Dublin continued into Friday morning.

The Irish foreign minister Simon Coveney tweeted on Friday morning, saying that a deal had been struck.

"We are making progress but not fully there yet. Talks are continuing through the night," EU Commission President Jean-Claude Juncker's spokesman Margaritis Schinas said earlier. "Tonight more than ever, stay tuned."

European Council President Donald Tusk was set to make a statement giving a "situational update" on Brexit early on Friday.

May, who flew to Brussels Friday morning to meet with Juncker, faced problems earlier this week over the Irish border issue.

Difficulties arose amid opposition from the small Northern Irish Democratic Unionist Party (DUP), which props up the UK's Conservative government.

Different paths within UK?

Amid hope that a deal had been agreed, the DUP — which wants to retain closer links to London than Dublin — expressed concern that a deal to allow an open border in Ireland would entail "regulatory divergence" for Northern Ireland from the UK.

Read more: The Irish border — what you need to know

Juncker spoke first to Irish Prime Minister Leo Varadkar and then to May on Thursday night, seeking to tweak the wording of the Irish border deal.

The EU has been calling for clarity on three key issues — the Irish border, the financial settlement, and the rights of EU citizens in the UK — before it agrees to start trade talks on future relations.

The talks have been made particularly urgent in light of a summit of EU leaders set to take place December 14-15, where the decision talks about a future deal would be given the green light.

cw,rc/ng/aos (dpa, AFP, Reuters)