The leader of the European Union's executive complained Friday that talks on Britain's departure from the bloc will take longer than expected, and demanded that Prime Minister Theresa May's government pay its divorce bill.

European Commission President Jean-Claude Juncker said the EU's British partners "are discovering, as we are day after day, new problems," and added "this process will take longer than initially thought."

A day after the EU's Brexit negotiator said talks on the divorce bill were deadlocked, Juncker insisted in Luxembourg that "they have to pay. They have to pay."

"If you are sitting in a bar and if you are ordering 28 beers, and then suddenly some of your colleagues is leaving and is not paying – that's not feasible," he said in English.

If you are sitting in a bar and if you are ordering 28 beers and then suddenly some of your colleagues is leaving and is not paying – that's not feasible. - Jean-Claude Juncker

He insisted the EU is not seeking outrageous sums, saying Britain's bill does not have to be settled "in an impossible way. I'm not in a revenge mood."

Various EU estimates suggest the bill could amount to 60 billion to100 billion euros ($88 billion to $148 billion Cdn). The British government has rejected such numbers.

Juncker's comments came as EU leaders, without May, prepare next week to launch preliminary talks on the outline of the future EU-UK relationship once Britain leaves on March 29, 2019.

In a draft summit statement seen Friday by The Associated Press, the leaders order EU ministers and Brexit negotiator Michel Barnier "to start internal preparatory discussions" on future ties.

This would allow the EU to move quickly on elements like trade relations if negotiators make "sufficient progress" by December on the terms of the EU-U.K. divorce agreement.

Negotiations are moving slowly. EU leaders insist progress must be made on Britain's divorce bill, the rights of citizens hit by Brexit and the future state of the Northern Ireland-Ireland border.

The leaders, who meet in Brussels on Oct 19-20, and again in mid-December, refuse to talk about future relations until that happens.

In the draft text, which could be modified, the leaders note that "while the U.K. has stated that it will honour its financial obligations taken during its membership, this has not yet been translated into a firm and concrete commitment from the UK to settle all of these obligations."