The UK must agree a "backstop" plan for the Northern Ireland border after Brexit as "a matter of some urgency", the EU's chief negotiator has warned.

Speaking after the latest round of negotiations, Michel Barnier said that without a detailed plan, "there will be no agreement".

The sticking point relates to what should happen to the Northern Ireland border if the UK and EU are unable to reach a trade deal that would see an open border maintained.

Speaking alongside Dominic Raab, the Brexit secretary, Mr Barnier said: "We must have a detailed backstop solution, which is legally operational, in the withdrawal agreement.

"The prime minister, Theresa May, committed herself to this, as have all the leaders of EU institution – the parliament for example."

He added: "It is a matter of some urgency. We have to work on drafting an operational backstop.

"This backstop is critical – its essential to conclude the negotiations. With no backstop there will be no agreement."

Mr Barnier said he had asked the UK to provide the technical data needed to plan how customs checks could work after Brexit.

Mr Raab said the UK was "committed" to agreeing a plan.

He added: "The solutions must be workable. They 've got to be workable for the communities living in Northern Ireland and living in the Republic of Ireland – the people affected in their daily lives by what Michel and I are negotiating on behalf of the EU and the UK at the moment."

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The EU has proposed a backstop plan that would see Northern Ireland in effect remain in the customs union and single market, therefore removing the need for border checks – but the UK government says any arrangement gives the region a different status to the rest of the country is unacceptable.

Instead, ministers have suggested a "customs arrangement" that would see the whole UK adopt the same tariffs as the EU for a time-limited period until a longer-term agreement is reached. But Brussels said this amounted to "cherry-picking" and has made clear it will not accept a backstop that is time-limited.

The issue has become one the the main sticking points during negotiations. A deal is needed by October to ensure the European Parliament and member states have enough time to ratify it before the UK leaves the bloc next March.

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Despite fears that time is running out, Mr Barnier said he was confident an agreement could be reached by the deadline and promised a "partnership without precedent" with the UK after Brexit.

He said: "We have, I think, all the necessary building bricks to build a close and effective relationship between the Union and the United Kingdom on a series of subjects which are very important for the citizens.

"Week after week and step by step we are eliminating subjects, bones of contention... I’m determined we’re going to find an agreement for an orderly withdrawal which is much better than the opposite and Dominic and I think it’s possible to reach that in October.”

Mr Raab also expressed confidence that the UK and EU would be able to reconcile their differences.