Michel Barnier says time is running out to secure an exit deal for the UK
Speaking to journalists at the summit of EU leaders taking place in Brussels, he said finding a solution to the Northern Irish border remains the biggest problem.
He added: "After Brexit, we want, the EU want, an EU-UK ambitious partnership, on trade as well as on security.
"But we have to base this partnership on our values and principles, respecting also the UK red lines. That means for us integrity of the single market, indivisibility of the four freedoms, autonomy of the decision making of the EU, and protection and respect of the fundamental rights of EU citizens. And this point is key for our future cooperation and security."
He said the EU is now waiting to see a 'white paper' promised by British Prime Minister Theresa May, after a special cabinet meeting at the Prime Minister's country residence Chequers, planned for July 5 and 6. However he said he "[hopes] it will contain workable and realistic proposals".
He added: "Let me mention once again that time is very short. We want a deal, and are working for a deal, but time is short and I'm ready to invite the UK delegation to come back and present next Monday."
It had been hoped that there would have been agreement on most matters by this stage as the EU's deadline for a final exit treaty to be ready is October. If the UK leaves with no deal next March then everything so far agreed for rights of Britons in the EU and EU27 citizens in the UK would collapse, leaving great uncertainty.
On the issue of the future UK/EU relationship Mrs May is said to be considering offering keeping the whole of the UK in the EU's single market just for goods [ie. not for services or the free movement of people], however this may not be acceptable to the EU.
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Comment: Jean Claude-Juncker says EU is getting ready for no-deal on Brexit