The Taoiseach Leo Varadkar has said the British Prime Minister Theresa May cannot keep coming back to Europe every few weeks looking for more Brexit concessions.
It is after Mrs May said there is the possibility of further assurances to get her MPs on board with the withdrawal agreement.
All sides are now stepping up preparations for a no-deal Brexit, with the Irish Government due to publish an updated plan next week.
Mr Varadkar said the EU will provide assurances for Mrs May, but the situation in the UK needs to get moving.
"We can't have situation whereby any negotiating party - and this is true for any treaty or agreement - comes back every couple of weeks, following discussions with their parliament, looking for something extra - looking for something more.
"You can't operate international relations on that basis".
He is also hopeful a further promise that the backstop will only be temporary will be enough.
"What I'm hoping will be the case is the very robust assurances that we've given in this communiqué - agreed by 27 governments last night, the European Commission and the European Council... will be sufficient for Westminster to ratify this agreement.
"If it's not, we'll have to take it from there".
On the extra assurances Theresa May is looking for Leo Varadkar has said the PM can’t be coming back every few weeks looking for more and EU leaders were keen to know from her if she thinks what they’ve offered will be enough to sway MPs pic.twitter.com/hon9CBE8Sc
— Sean Defoe (@SeanDefoe) December 14, 2018
EU leaders gathered in Brussels on Thursday for a European Council summit, amid continued opposition to the Brexit agreement in Westminster.
After late night talks, European leaders said there would be no re-negotiation of the withdrawal agreement.
They re-enforced the point that the backstop has always been designed to be a temporary measure and an 'insurance policy'.
Earlier, Mr Varadkar said he was very satisfied with the EU's decision not to offer more Brexit concessions.
Speaking before the second day of the summit, Mr Varadkar said the EU is always willing to offer clarifications on the deal.
However, he stressed: "What we won't be doing as a European Union is renegotiating the withdrawal agreement.
"Last night we confirmed that the backstop needs to be part of the withdrawal agreement - it's not just an Irish issue, it's a European issue. It's about protecting the peace, keeping the border open."
“The backstop is not just an Irish issue, it’s a European issue”. Leo Varadkar says he’s satisfied with the decisions of the EU Council last night pic.twitter.com/oX4ksJDne1
— Sean Defoe (@SeanDefoe) December 14, 2018
Mrs May, meanwhile, insisted that EU leaders left open the possibility for 'further clarifications'.
She said: "There is work still to do, and we will be holding talks in coming days about how to obtain the further assurances the UK parliament needs in order to be able to approve the deal.
"It is in the overwhelming interests of all our people in the EU and the UK to get this done, and as quickly as possible."
She also acknowledged having a 'robust' discussion with European Commission President Jean-Claude Juncker - an exchange that was caught on camera without sound, but is believed to have been over Mr Juncker's use of the word 'nebulous' to describe Brexit talks.
NEW - Two expert lipreaders tell 5 News that Theresa May accuses Jean-Claude Juncker of describing her as nebulous.
This is how the conversation went, according to the lipreaders: pic.twitter.com/IuP99fJiXG
— Channel 5 News (@5_News) December 14, 2018
Mrs May told reporters: "What came out of that was his clarity that he'd been talking, when he used that phrase, about a general level of debate... I've had further conversations with him through the morning."
"No re-negotiations"
European Council President Donald Tusk (R) talks to European Commission President Jean-Claude Juncker | Image: Dario Pignatelli/European Council/dpa
Speaking after Thursday's meeting, Mr Juncker insisted: "We can add some clarifications... to what has been agreed upon. But there will be no re-negotiations."
He added: "I do find it uncomfortable that there's an impression perhaps in the UK that it's for the EU to propose solutions - it is the UK leaving the EU.
"I would have thought it was rather more up to the British government to tell us exactly what they want."
European Council President Donald Tusk, meanwhile, noted that the backstop - if it is triggered at all - would only apply 'unless and until' another agreement is reached to avoid a hard border in Ireland.
Donald Tusk confirms nothing has changed about the backstop after tonight’s meeting. It’s a temporary measure designed to be in place unless and until a better deal is reached #Brexit pic.twitter.com/A2GFltWxE0
— Sean Defoe (@SeanDefoe) December 13, 2018
However, he also said: "The [EU] stands by this agreement and intends to proceed with its ratification. It is not open for renegotiation."
European leaders also called for work to prepare for a potential no-deal Brexit and "all possible outcomes" to be intensified.
Theresa May in Brussels | Image: Alastair Grant/AP/Press Association Images
Mrs May travelled to Brussels on Thursday only hours after surviving a Conservative Party confidence vote in Westminster.
A majority of MPs appear to oppose the deal, with parties such as the DUP - which is propping up Mrs May's government - calling for the backstop to be backed altogether.
A House of Commons schedule released on Thursday indicated that the postponed 'meaningful vote' on the Brexit deal may not take place until January - but Mrs May is likely to continue to struggle to sell the deal to its opponents before then.
Additional reporting: Sean Defoe and Jack Quann
