Brussels (AFP) - European Union leaders laid the ground Friday for the next phase of Brexit talks after British Prime Minister Theresa May urged them to seize a "new dynamic" in the negotiations.
The 27 leaders meeting in Brussels adopted negotiating guidelines for talks on the future relationship with Britain and approved a deal for a 21-month transition period.
"We are today making a decisive step in these difficult and extraordinary negotiations," the bloc's Brexit negotiator, Michel Barnier, said as he arrived for the summit talks.
"On this basis we will begin discussions with the UK for this future partnership which must respect the principles and the identity of the EU and the single market."
Britain is leaving the EU in March 2019, but negotiators this week agreed a transition deal that effectively maintains the relationship -- although London will have no voting rights -- until December 2020.
Britain's May, who attended the summit before leaving early Friday when the talks turned to Brexit, welcomed the approval, saying the transition deal brought "certainty".
"I believe there's a new dynamic now in the negotiations," she told reporters as she left.
"I believe we are approaching this with a spirit of cooperation, a spirit of opportunity for the future as well."
- No backtracking -
However, there are some key issues that still need to be resolved as part of the agreement that led to the transition deal, notably the future of the Irish border after Brexit.
The EU guidelines say that "negotiations can only progress as long as all commitments undertaken so far are respected in full".
They call for "intensified efforts" on the outstanding parts of the divorce, adding: "Nothing is agreed until everything is agreed."
Britain is leaving the EU's single market and customs union, but the prospect of new border checks between Northern Ireland and EU-member Ireland have sparked concerns about the fragile peace on the island.
The EU and Britain have agreed a "backstop" that Northern Ireland would remain part of the EU's customs union if there is no better idea -- but London is deeply opposed to this.
Just weeks earlier May had said no British premier could ever accept such an idea, which would meant cutting off Northern Ireland from the rest of the British economy.
She said on Friday: "We will now be sitting down and determining those workable solutions for Northern Ireland but also for our future security partnership and economic partnership."
Irish premier Leo Varadkar, who met May on the sidelines of the summit on Thursday, said he envisaged a trading relationship that was "so close that many of measures in the backstop may become unnecessary".
Days before the summit, EU President Donald Tusk had raised fears that some countries would not back the plan, with Spain in particular expressing concerns about the fate of the British territory of Gibraltar.
But he later announced that he had "good news" for May and officials said that Madrid had been placated by the addition of a special mention of Gibraltar in the guidelines.
May secured a diplomatic victory on Thursday after securing unanimous EU backing for Britain's assessment that Russia was "highly likely" responsible for a nerve agent attack on an ex-spy in the English city of Salisbury.