Latest: Theresa May urges EU to move on 'next stage' of Brexit negotiations

She confirmed she will be meeting European Council president Donald Tusk in the margins of the gathering later on Friday.

It follows Mr Tusk's warning that the EU needed greater clarity on the terms of Britain's withdrawal, including the divorce bill, by early December if there was to be any chance of leaders giving the go-ahead for phase two of the Brexit negotiations to start at their next summit later in the month.

Mrs May told reporters: "I will be seeing President Tusk here today, talking about the positive discussions we are having looking ahead to the deep and special partnership I want with the European Union.

"These negotiations are continuing but what I am clear about is that we must step forward together.

"This is for both the UK and the European Union to move onto the next stage."

Earlier: Theresa May will reaffirm Britain's ongoing commitment to European security as she faces further pressure from EU leaders to spell out how she intends to settle the UK's Brexit "divorce bill".

The Prime Minister will hold fresh talks on Friday with European Council president Donald Tusk during a summit in Brussels between the EU and former Soviet bloc "partner" states.

She was warned last week by Mr Tusk the EU needed greater clarity on the terms of Britain's withdrawal - including the financial settlement - by early December if there was to be any chance of leaders giving the go ahead for phase two of the Brexit negotiations to start at their next summit later in the month.

Mrs May is due to travel to the Belgian capital again on December 4 to meet European Commision president Jean-Claude Juncker in what is being seen as a final opportunity to meet Mr Tusk's deadline.

Mr Juncker said on Thursday that he was not yet in a position to say that sufficient progress had been made for a breakthrough at the European Council summit on December 14-15, but was hoping the process would "move forward" when he met Mrs May.

The Commission president said he was "not crazy enough" to be drawn on whether a £38 billion "divorce bill" offer expected from the PM would be acceptable to the 27 remaining EU states.

The Sun reported that Mrs May will demand a very swift agreement on a transition period after the date of Brexit in 2019 in return for the sum. And the paper reported that leading Brexiteers Michael Gove and Boris Johnson now believe that she will insist on the UK diverging from EU "regulatory harmonisation" after withdrawal.

Mrs May is also facing a demand from Irish premier Leo Varadkar for a written guarantee there will be no return to the "hard border" of the past between Northern Ireland and the Republic as the price of his support for the second phase of the negotiations to begin.

Since last week's EU gathering in Gothenburg, Sweden, the Cabinet has met to discuss what they would be prepared to pay to settle the "divorce bill", with ministers reportedly agreeing to double the sum originally put on the table by Mrs May to around £40 billion.

But it is thought she does not want to name a precise figure until she has a clear idea of what kind of trade deal is available with the remaining EU member states in the phase two negotiations.

Speaking ahead of Mrs May's talks with Mr Tusk, the Prime Minister's official spokesman played down suggestions it was a meeting to set out the divorce bill.

"I would not characterise it in that way," the spokesman said.

"We saw from his comments at the end of the press conference in Gothenburg that he (Mr Tusk) was hoping to meet the PM this week.

"They will be discussing progress towards the December council.

"There are a number of issues which I'm sure they will want to discuss - the financial settlement, that will be one of them, also of course Northern Ireland and citizens' rights."

With leaders from Armenia, Azerbaijan, Belarus, Georgia, Moldova, and Ukraine also due in Brussels on Friday, Mrs May will take the opportunity to highlight Britain's continued support for the region in the face of the threat from a resurgent Russia.

She is expect to point to the £50 million the UK is providing this year to the region to support projects like tax reform in Moldova and de-mining in Ukraine, with a further £100 million over the next five years to counter "disinformation".

"From agriculture in Ukraine to the tech sector in Belarus, there is a huge amount of potential in the Eastern neighbourhood that we should nurture and develop," she is expected to say.

"But we must also be open-eyed to the actions of hostile states like Russia which threaten this potential and attempt to tear our collective strength apart.

"This summit highlights the crucial importance of the European countries working together to protect our shared values and ideals.

"The UK may be leaving the EU but we are not leaving Europe, and we are unconditionally committed to maintaining Europe's security."