European Union chief Brexit negotiator Michel Barnier, right, and British Secretary of State for Exiting the European Union David Davis leave after a media conference at EU headquarters in Brussels on Thursday, Sept. 28, 2017. The EU and Britain concluded a fourth round of Brexit negotiations on Thursday. (AP Photo/Olivier Matthys)

BRUSSELS - The European Union's chief Brexit negotiator warned Thursday that talks on Britain's departure from the bloc are weeks, possibly months, away from making substantial progress, despite hailing a positive new momentum in the negotiations.

Britain is scheduled to leave the EU on March 29, 2019 — the first member country ever to do so — but the talks must be wrapped up by October 2018 to allow time for parliaments to ratify it.

More than a year since Britons voted to go, and six months after London triggered the two-year countdown to Brexit, the talks are still in a preliminary phase. Many EU leaders fear that time will run out, leaving a messy divorce that would be damaging to both Britain and its European partners.

After a fourth round of negotiations concluded in Brussels, Michel Barnier said: "We will need several weeks, even several months, to be able to see 'sufficient progress' on the principles of this orderly departure."

Britain's Brexit negotiator David Davis was more upbeat, and told reporters that the negotiations had "made important progress."

EU leaders insist the talks must make "sufficient progress" on Britain's financial settlement, the rights of citizens hit by Brexit and the status of the Ireland-Northern Ireland border before they can be broadened to include future relations and trade between Britain and the EU.

Britain the issues are intertwined and should be thrashed out together.

EU leaders, minus British Prime Minister Theresa May, must rule on whether and when "sufficient progress" has been made. They had been expected to do just that on October 19-20 at their next summit, but Barnier's assessment assures that this tentative deadline will be missed.

Barnier said Britain has not yet identified the amount of the financial commitments it will make as part of the divorce agreement, although it has agreed to pay its 2019 and 2020 budget share, part of the EU's long-term budget arrangement agreed on around five years ago.

"The only way to reach sufficient progress is that all commitments undertaken at 28 (member states) are honoured at 28," the former French government minister said.

Barnier and Davis acknowledged that they had failed to bridge differences over what role the European Court of Justice should play in the future. One of the main Brexit referendum campaign themes played on public discontent with the Luxembourg-based ECJ ruling on British interests.

"This is a stumbling block for the EU," said Barnier.

Still, he hailed the "new dynamic" that May's speech in Italy last week had inspired and the more detailed British proposals that had resulted from it.

Davis agreed that things had changed.

"We are making decisive steps forward," Davis said, adding that much progress was made on ensuring the rights of citizens who will be hit by Britain's departure. Those include 3 million EU citizens living in Britain and 1 million Britons living on the continent.

EU officials have previously said Britain's offer to EU citizens falls short of guaranteeing the rights they have now. Barnier said Thursday that progress had been made but a "big gap" remained in some areas.

In a rare joint statement, British trade unions and British employers called on the U.K. and the EU to offer more certainty to individuals and businesses. They said "after 15 months of human poker, the uncertainty facing 4 million European and U.K. citizens has become intolerable."

The Trades Union Congress and the Confederation of British Industry said "a clear guarantee of the right to remain for citizens in both the U.K. and EU27 is needed within weeks."

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Jill Lawless in London contributed to this story.

News from © The Associated Press, 2017