Irish Prime Minister Leo Varadkar said the UK must produce a concrete plan to ensure continued ease of mobility between the independent Republic of Ireland, an EU member, and Northern Ireland, one of the Brexit-bound UK's four countries.

"The EU 27 can't declare sufficient progress in the Brexit negotiations without firm and acceptable commitments on the border," Varadkar said after meeting with European Council President Donald Tusk in Dublin on Friday. They spoke ahead of a meeting of EU leaders later this month to decide whether Brexit negotiations have stalled indefinitely or can be allowed to advance.

Set to begin in 2019, Brexit would replace the freely crossed 310-mile (500-kilometer) frontier between the Republic of Ireland and Northern Ireland with a land border separating the European Union from the United Kingdom. British officials have said they want to maintain a "frictionless" flow of people and goods with no border posts, but have yet to put forth a plan for implementing that once the United Kingdom leaves the EU's borderless single market and tariff-free customs union.

If Britain does not provide such details, the European Union would not agree to start discussing future relations and trade. The European Union has imposed a number of punitive measures since a majority voted for Brexit in June 2016.

Earlier this year, activists set up a mock border to demonstrate the hassles to come

'Exposed and vulnerable'

The Democratic Unionist Party (DUP) in Northern Ireland has opposed one possible solution that would permit Northern Ireland to remain the UK's lone member of the EU's customs union following Brexit. And UK Prime Minister Theresa May relies on the DUP as a partner to her ruling Conservatives in her minority government.

Read more: Can Theresa May exploit Germany's woes in Brussels?

The EU will not hear any Brexit offer from the United Kingdom that Ireland does not approve of, Tusk said after Friday's talks with Varadkar. "If the UK offer is unacceptable for Ireland, it will also be unacceptable for the EU," Tusk said. He said the EU stood "fully behind" Ireland's demand to avoid a "hard border."

Any barrier to movement of people or goods could hurt economies on both sides — and threaten Northern Ireland's peace process. Trade has thrived since a 1998 accord abolished checkpoints and customs posts imposed during years of conflict. Thousands of people live on one side and work on the other, or cross daily to shop or socialize.

On Friday, Irish Foreign Minister Simon Coveney told reporters that Ireland finds itself "uniquely exposed and vulnerable to the consequences of Brexit."

"We have an all-island economy," Coveney said. "We cannot allow an unintended consequence of Brexit to be an undermining of that relationship in future," he added.

As in Scotland, some politicians in Northern Ireland have floated the idea of the country's withdrawal from the United Kingdom to avoid the consequences of Brexit.

Brexit timeline: Charting Britain's turbulent exodus from Europe June 2016: 'The will of the British people' After a shrill referendum campaign, nearly 52% of British voters opted to leave the EU on June 23. Polls had shown a close race before the vote with a slight lead for those favoring remaining in the EU. Conservative British Prime Minister David Cameron, who had campaigned for Britain to stay, acknowledged the "will of the British people" and resigned the following morning.

Brexit timeline: Charting Britain's turbulent exodus from Europe July 2016: 'Brexit means Brexit' Former Home Secretary Theresa May replaced David Cameron as prime minister on July 11 and promised the country that "Brexit means Brexit." May had quietly supported the Remain campaign before the referendum. She did not initially say when her government would trigger Article 50 of the EU treaty to start the two-year talks leading to Britain's formal exit.

Brexit timeline: Charting Britain's turbulent exodus from Europe March 2017: 'We already miss you' May eventually signed a diplomatic letter over six months later on March 29, 2017 to trigger Article 50. Hours later, Britain's ambassador to the EU, Tim Barrow, handed the note to European Council President Donald Tusk. Britain's exit was officially set for March 29, 2019. Tusk ended his brief statement on the decision with: "We already miss you. Thank you and goodbye."

Brexit timeline: Charting Britain's turbulent exodus from Europe June 2017: And they're off! British Brexit Secretary David Davis and the EU's chief negotiator, Michel Barnier, kicked off talks in Brussels on June 19. The first round ended with Britain reluctantly agreeing to follow the EU's timeline for the rest of the negotiations. The timeline split talks into two phases. The first would settle the terms of Britain's exit, and the second the terms of the EU-UK relationship post-Brexit.

Brexit timeline: Charting Britain's turbulent exodus from Europe July-October 2017: Money, rights and Ireland The second round of talks in mid-July began with an unflattering photo of a seemingly unprepared British team. It and subsequent rounds ended with little progress on three phase one issues: How much Britain still needed to pay into the EU budget after it leaves, the post-Brexit rights of EU and British citizens and whether Britain could keep an open border between Ireland and Northern Ireland.

Brexit timeline: Charting Britain's turbulent exodus from Europe December 2017: Go-ahead for phase 2 Leaders of the remaining 27 EU members formally agreed that "sufficient progress" had been made to move on to phase two issues: the post-Brexit transition period and the future UK-EU trading relationship. While Prime Minister Theresa May expressed her delight at the decision, European Council President Tusk ominously warned that the second stage of talks would be "dramatically difficult."

Brexit timeline: Charting Britain's turbulent exodus from Europe July 2018: Johnson, Davis resign British ministers appeared to back a Brexit plan at May's Chequers residence on July 6. The proposal would have kept Britain in a "combined customs territory" with the EU and signed up to a "common rulebook" on all goods. That went too far for British Foreign Minister Boris Johnson and Brexit Secretary David Davis, who resigned a few days later. May replaced them with Jeremy Hunt and Dominic Raab.

Brexit timeline: Charting Britain's turbulent exodus from Europe September 2018: No cherries for Britain May's Chequers proposal did not go down well with EU leaders, who told her at a summit in Salzburg in late September that it was unacceptable. EU Council President Tusk trolled May on Instagram, captioning a picture of himself and May looking at cakes with the line: "A piece of cake perhaps? Sorry, no cherries." The gag echoed previous EU accusations of British cherry-picking.

Brexit timeline: Charting Britain's turbulent exodus from Europe November 2018: Breakthrough in Brussels EU leaders endorsed a 585-page draft divorce deal and political declaration on post-Brexit ties in late November. The draft had been widely condemned by pro- and anti-Brexit lawmakers in the British Parliament only weeks earlier. Brexit Secretary Dominic Raab resigned along with several other ministers, and dozens of Conservative Party members tried to trigger a no-confidence vote in May.

Brexit timeline: Charting Britain's turbulent exodus from Europe December 2018: May survives rebellion In the face of unrelenting opposition, May postponed a parliamentary vote on the deal on December 10. The next day, she met with German Chancellor Angela Merkel to seek reassurances that would, she hoped, be enough to convince skeptical lawmakers to back the deal. But while she was away, hard-line Conservative lawmakers triggered a no-confidence vote. May won the vote a day later.

Brexit timeline: Charting Britain's turbulent exodus from Europe January 2019: Agreement voted down The UK Parliament voted 432 to 202 against May's Brexit deal on January 16. In response to the result, European Council President Donald Tusk suggested the only solution was for the UK to stay in the EU. Meanwhile, Britain's Labour Party called for a no-confidence vote in the prime minister, her second leadership challenge in as many months.

Brexit timeline: Charting Britain's turbulent exodus from Europe March 2019: Second defeat for May's deal May tried to get legal changes to the deal's so-called Irish backstop in the weeks that followed. She eventually got assurances that the UK could suspend the backstop under certain circumstances. But on March 12, Parliament voted against the revised Brexit deal by 391 to 242. EU leaders warned the vote increased the likelihood of a no-deal Brexit. Two days later, MPs voted to delay Brexit.

Brexit timeline: Charting Britain's turbulent exodus from Europe March 2019: Extension after second defeat Following the second defeat of May's divorce deal, the European Council met in Brussels on March 21 to decide what to do next. EU leaders gave May two options: delay Brexit until May 22 if MPs vote for the withdrawal deal or delay it until April 12 if they vote against the deal. If the deal were to fail again in Parliament, May could ask for a long extension.

Brexit timeline: Charting Britain's turbulent exodus from Europe March 2019: Brexit deal rejected a third time On March 29, the day that the UK was supposed to leave the EU, British lawmakers voted for a third time against May's deal — rejecting it this time with a vote of 344 to 286. Following the latest defeat, May approached the main opposition Labour leader Jeremy Corbyn in an attempt to find a compromise, angering hardline Brexiteers in her own Conservative party.

Brexit timeline: Charting Britain's turbulent exodus from Europe April 2019: Brexit delayed until Halloween With the April 12 deadline looming after the third defeat of May's deal, EU leaders met again in Brussels to discuss a second delay. The only question was how long should it be? In the end, the UK and EU agreed to a "flexible" extension until October 31 — which can end sooner if the Brexit deal is approved. The UK had to take part in EU elections in May because their exit wasn't secured in time.

Brexit timeline: Charting Britain's turbulent exodus from Europe May 2019: Prime Minister Theresa May resigns Weeks of talks between Prime Minister Theresa May and the Labour party to reach a deal proved unsuccessful and further eroded her political capital. She triggered an angry backlash from her party after she tried to put the option of a second referendum on the table. The series of failures led May to announce her resignation, effective June 7, in an emotional address.

Brexit timeline: Charting Britain's turbulent exodus from Europe June 2019: Search for a new prime minister After Theresa May announced on June 7 that she would leave office, other members of her Conservative party began clamoring for the top job. Within a month, the leadership battle came down to Jeremy Hunt (left), an EU proponent who fears a no-deal scenario, and Boris Johnson (right), one of the main proponents of Brexit.

Brexit timeline: Charting Britain's turbulent exodus from Europe July 2019: Prime Minister Boris Johnson At the end of July 2019, Johnson was officially named Theresa May's successor as British prime minister. "We are going to energize the country, we are going to get Brexit done by October 31," he said after he was elected leader of the Conservative Party.

Brexit timeline: Charting Britain's turbulent exodus from Europe September 2019: Johnson's election threat Conservative rebels and opposition MPs backed efforts to delay an October 31 Brexit deadline in fear of a no-deal departure. In response, Johnson called for a general election, saying his government cannot rule without a mandate after he stripped 21 rebel MPs of their Conservative status. The Labour Party said it would not back elections until legislation to block a no-deal Brexit was in place.

Brexit timeline: Charting Britain's turbulent exodus from Europe September 2019: Prorogation 'unlawful' In late September, Britain's highest court ruled that Johnson's decision to suspend Parliament ahead of the UK's planned exit was unlawful. "This was not a normal prorogation in the run-up to a Queen's Speech," said the Supreme Court. Political rivals immediately called on Johnson to leave his post. Johnson said he would abide by the court ruling, though said he "strongly" disagreed.

Brexit timeline: Charting Britain's turbulent exodus from Europe October 2019: A new deal British Prime Minister Boris Johnson managed to secure a deal with European negotiators that would allow the UK to leave the EU in an orderly manner. The deal received unanimous backing from the leaders of 27 other member states. But an attempt to get the UK Parliament to sign off on the deal failed. Instead, Parliament pushed for the Brexit deadline to be extended until the end of January 2020.

Brexit timeline: Charting Britain's turbulent exodus from Europe December 2019: Lawmakers vote for Johnson's Withdrawal Bill On December 22, UK lawmakers vote for Prime Minister Johnson's European Union withdrawal bill, which will see a leave date of January 31 2020 enshrined in law. Getting a majority to vote to pass the bill in the lower house has proven a major sticking point for the PM, but following a general election Johnson's Conservative party won control of the house and the bill passed with a 124 majority.



mkg/cmk (Reuters, AFP, dpa, AP)