Update 3.07pm: The "moment of truth" in Brexit negotiations is approaching and the European Union hopes for agreement on so-called withdrawal issues "in the next few days", Brussels' chief negotiator has said.
Michel Barnier called for "real, sufficient progress" on the Brexit "divorce bill", citizens' rights and the Irish border, so that EU leaders can green-light talks on trade and a transition period before Christmas.
He spoke as Foreign Affairs Minister Simon Coveney stressed that all EU27 leaders agree that trade talks cannot start unless Britain offers further assurances there will be no hard border with Northern Ireland.
Britain's Prime Minister Theresa May has been given until December 4 to come up with further proposals on the withdrawal issues so Mr Barnier can recommend to leaders at the December 14-15 European Council summit that enough progress has been made for trade talks to begin.
At an EU summit in Tallinn, Estonia, Mr Barnier said: "I do hope in the next few days we will come up with an agreement on principles, and a real agreement.
"We need to have real, sufficient progress in the three key areas where the UK's decision has created a lot of uncertainty and fear even."
He added: "The moment of truth is approaching, we have a council under the Estonian presidency on December 14 and 15, and I really hope that will be the point where we will see real, sufficient progress on the conditions of our separation.
"And that will allow me to recommend the opening up of the next two phases of negotiations, first of all on the transition period and then on the future relationship."
Amid fears there could be a return to a hard border in Ireland given the UK Government's commitment to leaving the European single market and customs union, which allow for frictionless trade, the Frenchman said: "We don't want to be putting up barriers again and we need furthermore to maintain the integrity of the single market."
On the divorce bill, he said Britain must honour its commitments for the EU budget between 2014 and 2020, which Mrs May has already signalled she will do.
"We have a programme from 2014 to 2020 and I have said we are not willing to pay, the 27 are not willing to pay what has been decided by the 28 and so we are asking for the UK to play its part, to honour its commitments for that period," Mr Barnier said.
And on the rights of EU nationals in the UK and British expats in Europe, he said: "We have done a lot, but we need to ensure that we clearly secure their rights reciprocally and that's why we need a role for the European Court of Justice."
Mr Coveney said Ireland will not need to use its veto to prevent progress in talks because EU negotiators will block it themselves if the UK does not offer a workable solution on the Irish border.
He said he had received personal assurances from senior EU figures Mr Barnier, Donald Tusk and Jean-Claude Juncker on Friday that Brussels would hold firm on this demand.
"They have repeated the message that Ireland's problems are the EU's problem, so Ireland is not going to be isolated and forced to use a veto," said Mr Coveney.
EU leaders insist a hardening of the border is inevitable if the UK leaves the single market and customs union, as checks will be required to monitor movement between jurisdictions operating under two different regulatory systems.
One solution offered by Europe is the suggestion Northern Ireland would continue to comply with EU regulations post-Brexit but this has been rejected by the UK Government.
Any arrangement which appeared to give Northern Ireland a separate status would also be strongly resisted by the Democratic Unionists (DUP), whose 10 MPs are effectively keeping Mrs May in Downing Street after she lost her majority in the general election.
Asked about the prospect of movement on the border issue, the PM's official spokesman said Britain is "firmly committed" to avoiding a physical frontier.
He added: "In order to be able to see what the solution is going to finally look like, we need to understand what the future trading relationship is going to be, because the two things are obviously related. We want to get on to talking about trade as soon as possible."
The PM's spokesman gave short shrift to suggestions that the problem could be resolved by allowing Northern Ireland to continue to observe the rules of the customs union, saying: "This has been raised numerous times and we've been clear that the United Kingdom as a whole is leaving the single market and is leaving the customs union."
He added: "We have reached agreement on continuing free movement of people over the border and we are focusing on finding a solution in relation to goods."
Former taoiseach Bertie Ahern has suggested the only solution is to introduce technology to manage multinational trade while turning a blind eye to lower-level cross-frontier movement in areas such as agriculture.
Update 11.50am: All leaders of the EU 27 are in agreement that Brexit talks will not proceed to phase two unless the UK offers further assurances on the Irish border, Ireland's foreign minister has said.
Simon Coveney said Ireland will not need to use its veto to prevent negotiations moving to the issue of future trading relations because EU negotiators will themselves block the move if the UK does not offer up a workable solution ahead of December's crunch summit in Brussels.
Mr Coveney said he received personal assurances from senior EU figures Michel Barnier, Donald Tusk and Jean Claude Juncker on Friday that the EU would hold firm on this demand.
"They have repeated the message that Ireland's problems are the EU's problem, so Ireland is not going to be isolated and forced to use a veto," said Mr Coveney.
"We are part of an EU negotiating team that is very clear on this issue - there needs to be more progress on the Irish issues between now and the 14th of December and if that doesn't happen we won't be moving on to the phase two discussions, which is where everybody wants to be, including Ireland."
In an interview on RTE radio, he added: "We can't allow a situation to develop where we move into phase two of discussions on Brexit in the hope that somehow the border is going to be resolved without having any credible understanding as to how that's going to be done."
The issue of how to maintain the a "soft" border between Northern Ireland and the Republic of Ireland is a key stumbling block in Brexit negotiations, and Prime Minister Theresa May has just a week to meet a European deadline to make progress before trade talks can begin.
EU leaders insist that a hardening of the border is inevitable if the UK leaves the single market and customs union, as checks will be required to monitor movement between jurisdictions operating under two different regulatory systems.
One solution offered by Europe is the suggestion Northern Ireland would continue to comply with EU regulations post-Brexit. The UK government has rejected such a concept as a non-runner.
Any arrangement which appeared to give Northern Ireland a separate status would also be strongly resisted by the Democratic Unionists, whose 10 MPs are effectively keeping Mrs May in Downing Street after she lost her majority in the general election.
Mrs May has been given until December 4 to come up with further proposals on issues including the border, the Brexit divorce bill and citizens' rights.
Moving on to phase two of the negotiations, on trade, can only happen if all 27 leaders of the remaining EU countries agree at the European Council summit on December 14-15 that "sufficient progress" has been made on the first set of issues.
Mr Coveney said that the "full picture" would only become clear in phase two, but he said much more work was needed in phase one.
"If you basically move from one customs union into another customs union when you move from Ireland into Northern Ireland then there has to be customs checks, there is no way of avoiding that," he said.
Update 10.30am: EU leaders united over demands for Irish border assurances
A Brexit-backing MP has been compared to Donald Trump after saying Ireland will have to pay if it wants to erect a physical border with Northern Ireland if Britain leaves the European Union with no deal.
British Labour's Kate Hoey claimed "we won't be putting up the border" to govern EU-UK business through Northern Ireland, even if Britain leaves without agreeing new trade rules with Brussels.
And her remark that "they'll have to pay for it" drew immediate comparisons with the United States president, who has pledged to build a wall on the border with Mexico, which he claims will also pay for it to be built.
Ms Hoey told BBC Radio 4's Today programme: "We're not the ones who are going to be putting up the physical border.
"If it ends up with a no dea,l we won't be putting up the border - they'll have to pay for it, because it doesn't need to happen."
Reacting to the MP's comments, Cambridge University classicist Mary Beard tweeted: "When Kate Hoey on @BBCr4today talks about the Irish having to pay for putting up the border between N and S Ireland if there is to be one, she sounds to me dangerously like Mr Trump and Mexico."
When Kate Hoey on @BBCr4today talks about the Irish having to pay for putting up the border between N and S Ireland if there is to be one, she sounds to me dangerously like Mr Trump and Mexico.— mary beard (@wmarybeard) November 27, 2017
The row over how to maintain a "soft" Irish border has become a key sticking point in Brexit negotiations because the Government has committed to leaving the single market and customs union, which allow for frictionless trade among members.
UK Prime Minister Theresa May has just a week to meet a European deadline to make progress on the issue, along with the divorce bill and citizens' rights, if she wants EU leaders to agree at the European Council summit on December 14-15 to move on to trade talks.
Ms Hoey said both sides should look to Switzerland and Norway, which are outside the EU but have close trade relationships with it, for solutions to the Irish border issue.
She said: "A lot of the technology, at the Swiss border and in Norway, is done actually away from the border - and of course the Prime Minister has said that she doesn't want cameras at the border.
"There are ways of doing this... why don't the Irish government actually become more positive about this and start looking at solutions with their closest neighbour and closest partner? After all, we are a friend of the Republic of Ireland, the relations have never been as good.
"And yet on this issue it seems like they are more concerned to keep the rest of the EU satisfied than actually looking at concrete positive proposals."
Ms Hoey also claimed Ireland would look to quit the EU once it saw Britain making a success of Brexit.
"We joined the EU together, you joined when we joined, and I wouldn't be a bit surprised if we leave and when we're very successful that you don't start looking as well," she said.
Update 9.45am: The only solution to Ireland's Brexit border row with Britain is to introduce technology to manage multinational trade while turning a blind eye to lower-level cross-frontier movement, former taoiseach Bertie Ahern has suggested.
The issue of how to maintain the "soft" border between Northern Ireland and the Republic of Ireland after Brexit is a key stumbling block in Brexit negotiations, and UK Prime Minister Theresa May has just a week to meet a European deadline to make progress before trade talks can begin.
Cabinet minister Liam Fox has said the issue cannot be resolved until it is known what the "end state" of the UK-EU trade relationship will be after Brexit 2019, but Dublin has called for firm guarantees amid fears that the Government's commitment to leaving the single market and customs union could see a return to a hard border.
Mr Ahern said the only option appeared to be using technology to manage a soft border governing EU-UK trade between Ireland and Northern Ireland, while simply ignoring lower level commerce in areas like agriculture.
"Our economy is relatively small, a huge amount of the trade is multinationals; it should be possible, I think, to do that by technology," he told BBC Radio 4's Today programme.
"But of course, when you come down to agriculture and smaller items, I don't think technology would work.
"One thing we do not want, can't have, is back to a physical border."
He added: "Theresa May, take her at her word, she's confidently said she doesn't want a physical border, the EU don't want a physical border, the Irish Government don't.
"So you're left down with the one alternative - to make technology work in most cases and to throw a blind eye to those areas that can't come in within technology."
Earlier: The Irish government has denied threatening to derail the Brexit negotiations but insisted it would remain "resolute" in its stance over the border row with the UK.
Theresa May has just a week to meet a European Union deadline to make progress on key Brexit stumbling blocks, including the handling of Northern Ireland's border, but Cabinet minister Liam Fox said the issue could not be finally resolved until trade talks with Brussels have progressed.
Dr Fox said a final position could not be reached until it was known what the "end state" of the UK-EU relationship will be after the 2019 separation, but Dublin has indicated trade talks could be held up unless firm guarantees on the border are given by the UK Prime Minister.
Foreign Affairs Minister Simon Coveney dismissed a claim from Ukip that Ireland was threatening the UK, but insisted that his country must be protected in the Brexit process.
He said: "Ireland is not threatening anybody, least of all a friend, but we remain resolute in our insistence on a sensible way through Brexit that protects Ireland."
Dublin has said that if either the whole of the UK or just Northern Ireland remains in the single market and customs union then there would be no problem with maintaining the current soft border arrangements - a proposal ruled out by the UK Prime Minister.
Mrs May has been given until December 4 to come up with further proposals on issues including the border, the Brexit divorce bill and citizens' rights if European leaders are to give the green light to moving on to the next phase of negotiations covering the future trading relationship between the UK and Brussels.
International Trade Secretary Dr Fox said: "We don't want there to be a hard border but the UK is going to be leaving the customs union and the single market."
He told Sky News's Sunday with Niall Paterson: "We have always had exceptions for Ireland, whether it's in our voting rights, our rights of residence in the UK, we have always accepted a certain asymmetry and that will have to be part of whatever agreement we come to with the European Union but we can't come to a final answer to the Irish question until we get an idea of the end state.
"And until we get into discussions with the EU on the end state that will be very difficult, so the quicker that we can do that the better and we are still in a position where the EU doesn't want to do that."
He blamed the European Commission's "obsession" with forging a closer union for the delays in the Brexit talks, which the UK hopes will move on to discussing trade after a meeting of EU leaders on December 14-15.
European Affairs Minister Helen McEntee acknowledged that some of the final details would have to be dealt with in the next phase of Brexit talks but the UK must come forward with further proposals now to achieve the aim of maintaining a soft border.
Progress on to phase two of the negotiations can only happen if all 27 leaders of the remaining EU countries agree "sufficient progress" has been made on the first set of issues.
Ms McEntee told Channel 4 News: "We cannot say that there is sufficient progress on the Irish issue when there has not been.
"Theresa May's speech in Florence was very welcome, the commitment to not return to a hard border on the island of Ireland is welcome.
"However if all of the options that we feel can make that possible have been taken off the table then we need them to produce something else that will give us confidence, moving into phase two, that this can actually be achieved. To date this has not happened.
"But obviously I would hope, we need to be optimistic, that negotiations can continue before the December council meeting and that we can see some solution to this."
Any arrangement which appeared to give Northern Ireland a separate status would be strongly resisted by the DUP, whose 10 MPs are effectively keeping Mrs May in Downing Street after she lost her majority in the general election.