London - Negotiations regarding Brexit should "accelerate over the months to come" agreed British Prime Minister Theresa May and European Commission President Jean-Claude Juncker after a working dinner Monday.

"The working dinner took place in a constructive and friendly atmosphere," read the joint statement, noting that the two also discussed the Iran nuclear deal and terrorism in Europe, among talk about "global challenges."

Lack of progress

The meeting comes against the backdrop of deadlock in the talks about the terms of Britain's departure from the bloc. According to the statement, one of the topics discussed was an EU summit planned for later this week, where Brexit was supposed to be one of the main topics.

However, lack of progress in the divorce proceedings have raised questions about whether it even makes sense to turn to the topic at that level at this point.

News of the dinner had come as a surprise to British political correspondents, although May's office insisted the meeting had "been in the diary for weeks."

May was accompanied by Brexit Secretary David Davis, while Juncker came with the EU's chief negotiator, Michel Barnier.

Telephone diplomacy

Britain, a member of the EU since 1973, is the first country ever to begin procedures for leaving the bloc, following a referendum last year.

Ahead of Monday's dinner, May telephoned French President Emmanuel Macron and Irish Prime Minister Leo Varadkar to discuss Brexit and other issues.

"On Brexit, they discussed progress in the negotiations and looked ahead to this week’s [EU leaders' summit]," May's office said of the call to Macron.

It said May and Varadkar also "discussed the importance of maintaining constructive progress in the negotiations," agreeing to continue discussions at the summit.

May reiterated her government’s commitment to protecting the Belfast Agreement and the Common Travel Area after Brexit, it said.

The 1998 Belfast Agreement, also known as the Good Friday Agreement, paved the way for power-sharing between Republicans and Unionists after decades of sectarian violence in Northern Ireland.

The Common Travel Area allows Irish and British citizens to cross the Northern Ireland border without a passport and grants mutual voting rights in the two countries.

"Disturbing" deadlock

May also spoke to German Chancellor Angela Merkel by phone early Sunday, reportedly urging her to intervene to end the stand-off at the two-day summit.

Downing Street said May and Merkel had agreed on the "importance of continued constructive progress" in Brexit talks.

Last week's negotiations ended in stalemate after Britain failed to provide specifics on a financial settlement with the bloc, with Barnier calling it a "disturbing" deadlock.

Brussels has refused to go ahead with talks on a future trading relationship without "sufficient progress" on Britain's divorce bill, as well as the key issues of expatriates' rights and the Irish border.

Britain has, however, insisted that the talks be broadened to include the future relationship between Brussels and London, including trade.