The Taoiseach has accused the UK of stalling progress in Brexit negotiations and warned of the consequences of not striking a deal on the border.

Leo Varadkar suggested other countries will baulk at signing trade deals with the UK after Brexit if British Prime Minister Theresa May fails to honour commitments made to the EU on the Irish issue.

Mr Varadkar's comments came amid a stand-off over how to avoid a hard border on the island when the UK leaves the EU.

Both sides have agreed to include a so-called "backstop" option in the withdrawal treaty, which would commit the UK to align with an EU regulatory framework in the absence of a wider trade deal.

But the shape of that fallback remains a sticking point, with the EU rejecting a UK contention that it should only be temporary, even if a broader agreement fails to materialise.

Mr Varadkar urged the EU to continue to "stand behind Ireland" on the border issue.

He made the remarks in Dublin ahead of a visit to the city by European Commission president Jean Claude Juncker and EU chief negotiator Michel Barnier tomorrow.

"It is our view that we haven't seen sufficient progress from the UK in the last couple of months," said the Taoiseach.

"We had a good political agreement in December. We had further progress in March where they accepted there had to be a backstop as part of the withdrawal agreement.

"But since then, quite frankly, progress has stalled, and what I want all of Europe to do is to continue to stand behind Ireland and say to the UK they have to honour the commitments they made.

"And you know the UK is a country that's talking about going global, talking about making trade deals all over the world.

"How could anyone make a deal with a country that doesn't stand by its commitments?"

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The leaders of Sinn Féin have also accused the British government of playing a game of chicken over the border following a meeting with Mrs May.

Party leader Mary Lou McDonald and vice-president Michelle O'Neill were in London for a meeting with Mrs May on the key Brexit sticking point.

Ms McDonald said: "Despite all of the rhetoric Theresa May has drawn a blank by way of response to those issues, so we believe that there's game playing, there's brinksmanship and that the Tory government are playing a game of chicken with Brexit and with Ireland. We find that unacceptable."

She also reiterated Sinn Féin's call for Mrs May to grant Northern Ireland special status, allowing it to remain in the customs union and the single market.

Mrs McDonald added: "The British government knows what the answer is. They know precisely what the answer is but they're playing games and I think certainly patience has run out with that approach. It's dangerous, it's reckless."

EU leaders will next week call on member states, companies and all stakeholders to increase their preparedness for a 'no deal' scenario in the negotiations.

In a separate statement last night, Mr Barnier said serious divergences remained on the Irish backstop to avoid a hard border.

Next week's European Council has long been seen as critical point at which the UK would have to have made substantial progress on the Irish issue.

London has put forward a UK-wide backstop idea, in which Britain as a whole would remain in the customs union for a temporary period in order to avoid customs checks on the border between Ireland and the UK and along the Irish Sea.

However, the European Commission and other member states have all but rejected it.

Guy Verhofstadt, the European Parliament's chief Brexit co-ordinator, has said plans for a temporary backstop are "not acceptable".

Last night, EU and UK negotiators said they had made some progress on non-controversial aspects of the Withdrawal Agreement.

In a joint statement both parties said they recognised that the backstop would have to involve both customs and the alignment of EU rules on the single market, in line with paragraph 49 of last December's Joint Report.

They also agreed that the backstop would have to be given legal effect.

But in a separate statement, Mr Barnier said serious divergences remained and it is clear that this increases the prospect of a breakdown in the negotiations over Ireland. 

Leaked draft conclusions of next week's summit include a call to all EU member states and stakeholders to accelerate their readiness for a no deal scenario.