Taoiseach Leo Varadkar has ruled out formal three-way talks between the UK, Ireland and the EU to look at Theresa May's Brexit offer.

Mr Varadkar said it was not in the Republic's interests to take part in such talks regarding the withdrawal of Britain from the EU, and that what was needed was for Downing Street to produce more detailed proposals.

The comments came after the British prime minister on Sunday suggested Mr Varadkar had agreed to form three-way talks to look at the Irish border element of the proposals she outlined on Friday.

Mrs May set out her strategy for negotiations on Britain's future relationship with the EU in a high-profile speech in London.

It will be put to the test this week as negotiations between British and European Union officials resume in Brussels.

The taoiseach said: "There won't be tripartite or three-way talks.

"What will happen is that there will be talks between the EU 27 and the UK, and Ireland is part of the EU 27 and we're much stronger by the way as one of 27."

Good meeting this morning with @MaryLouMcDonald and @moneillsf @sinnfeinireland - essential to listen to all voices in Northern Ireland. Meeting @DUPleader tomorrow. Working to ensure the #UK's orderly withdrawal #Brexit pic.twitter.com/ckNDwO1eeS — Michel Barnier (@MichelBarnier) March 5, 2018

Mr Varadkar added consultations could take place between the two governments about issues that are unique to the Republic.

"We will of course have negotiations about what could be done to avoid a hard border, but what we won't be getting into is a negotiation with the UK, or a three-way negotiation," Mr Varadkar said.

"That's not in our interest and not the way that this can be concluded."

The taoiseach told RTE's Morning Ireland programme that he gave Mrs May's Brexit speech on Friday a guarded welcome, but that detail was now needed from the UK Government.

"What we want is not so much principles and aspirations and red lines," Mr Varadkar said.

"What we want is detail, written down in black and white that can be codified into law and that is what is required."

Mrs May's speech earned her breathing space from warring Remain and Leave factions in the Conservative Party, but her plans for maintaining a soft border while leaving the customs union were thrown into doubt when Tánaiste and foreign minister Simon Coveney said the EU may not accept her proposals.

The technical negotiations in Brussels from Monday to Wednesday will focus on the issue alongside a proposed transition period and other withdrawal issues including the financial settlement and citizens' rights, on which disagreements still need to be ironed out.

Mrs May is hoping to get a post-Brexit transition period signed off at the European Council summit of EU leaders on March 22-23, clearing the way for exploratory talks on trade.

But tensions over the border issue remain and could hold up agreement.

Amid the ongoing row over the border, Sinn Féin leaders Mary Lou McDonald and Michelle O'Neill travelled to Brussels on Monday to meet EU chief negotiator Michel Barnier.

After what she described as a "frank, productive and positive" meeting with Mr Barnier, Mrs McDonald voiced support for the taoiseach's stance.

"The taoiseach is absolutely correct to say that the substantive negotiation is between the British government on one hand and the EU member states collectively on the other and in our view it is important to maintain that dynamic," she said.

The Sinn Féin president added: "The ball is now in Mrs May's court, the ball is now in the court of the British, who say they don't like what they have seen, they don't like the solution advanced by Europe, if they don't like that we would like to know what is their solution."

Mrs McDonald said Mr Barnier understood the importance of resolving the border problem.

"I am happy to say we have a shared understanding that there cannot be a withdrawal agreement, much less an agreement on any future relationship between Britain and the European Union, in the absence of an answer to the Irish question," she said.

Mr Barnier, who is due to meet DUP leader Arlene Foster and deputy leader Nigel Dodds in Brussels on Tuesday, said his discussions with Sinn Féin had been positive.

He tweeted: "Essential to listen to all voices in Northern Ireland."

Mrs May has rejected Brussels proposals that would see Northern Ireland kept in an effective customs union with the EU as a fallback in case other solutions cannot be found.

She has proposed technological solutions and an exemption from new restrictions on the 80% of cross-frontier trade carried out by smaller businesses.

But on Sunday, Mr Coveney told BBC One's The Andrew Marr Show he was "not sure that the European Union will be able to support" the plan, as it would be worried about protecting the integrity of the single market.

Mrs May's de facto deputy, Cabinet Office minister David Lidington, said her speech was an "ambitious opening bid" and suggested the border proposals could be tweaked.