The European Union has given the UK just two weeks to clarify how it plans to settle its divorce bill.
Chief EU negotiator Michel Barnier imposed the deadline this afternoon, in a move likely to heap more pressure on British Prime Minister Theresa May over the progress of the discussions.
Speaking at a press conference following the completion of the sixth round of Brexit talks, Mr Barnier said clarification on the bill would be needed within the next two weeks for talks to move forward.
Mrs May had previously voiced a "degree of confidence" that phase-two Brexit talks could start before Christmas.
The latest round of talks again focused on the three key issues facing negotiators - the Irish border, citizens rights and the so-called "divorce bill."
This afternoon, Britain's Brexit Secretary David Davis warned that any deal cannot create a new border within the UK.
His comments come after an EU Commission position paper warned that Northern Ireland must remain in the single market if a hard border is to be avoided in Ireland.
The paper warned that the only way to maintain the Common Travel Area (CTA) and protect the Good Friday Agreement is for Northern Ireland to remain in both the single market and the customs union.
Two week deadline
This afternoon, asked to confirm reports that the EU needed clarifications or more concessions from the UK before talks can move on to phase two, Mr Barnier gave a one word answer: "Yes."
He said only "real and sincere progress" on the three key issues would be enough.
Failing that, he warned, negotiations on Britain's future relationship with the EU "will be put back."
Mr Davis meanwhile called for Brussels to show "flexibility, creativity and imagination."
He said the UK was "ready and willing to engage as often and as quickly as is needed to secure this outcome over the weeks remaining ahead of the December European Council."
The Council meeting where EU27 leaders will decide if "sufficient progress" has been made begins on December 14th.
Meanwhile, the Tánaiste has agreed to set up a working group on business supports to deal with the challenges posed by Brexit following a meeting with the EU Competition Commissioner Margrethe Vestager in Brussels.
Minister Frances Fitzgerald said the working group would enable her officials to work with the Commission on an ongoing basis with a view to achieving, " potential future supports for Irish business."
“The Commission acknowledges the unique exposure of Irish-based businesses to Brexit," said Minister Fitzgerald.
"We agreed that it is essential that Ireland is able to respond in a timely fashion to the likely challenges ahead.
"The working group will help ensure that we are in a position to respond to companies’ needs in an agile way, should the need arise."
The group is due to meet for the first time within the next two weeks.