Brexit is the "challenge of this generation," Irish taoiseach (prime minister) Leo Varadkar said on Friday.
Varadkar's comment came during his first official visit as Ireland's new head of government to the U.K.'s Northern Ireland region.
The island of Ireland is set to be further divided when the U.K. -- including Northern Ireland -- leaves the EU in 2019. The Republic of Ireland will remain an EU member state.
Varadkar's short tenure as Irish leader so far has seen a marked hardening in Dublin's attitude to Britain's Brexit issues, with the taoiseach last week saying his government was not interested in "designing a border for the Brexiteers".
An Irish parliamentary report released earlier this week also raised the issue of building a post-Brexit all-Ireland state, completely independent from the U.K.
In a keynote speech at Queen's University Belfast on Friday, Varadkar said Britain's exit from the EU will affect all aspects of life in Northern Ireland, where a majority of voters in the June 2016 referendum chose to remain in Europe.
"The Brexit negotiations are well under way in Brussels. And, to quote [EU negotiator] Michel Barnier, the clock is ticking," he added.
Speaking about the expected effects of Brexit, Varadkar said "every single aspect of life" in Northern Ireland would be influenced by the ending of the U.K.'s 44-year membership of the EU.
"The three key issues are citizens' rights, the financial settlement and issues relating to Ireland. It is my fervent hope that progress will have been made, but I do not underestimate the challenges we face," Varadkar said.
-Peace agreement
The taoiseach also raised concerns about Brexit's possible destabilizing effects on a 1998 peace deal which largely ended decades of sectarian violence in Northern Ireland.
"For our part, the Irish government will discharge our responsibilities as co-guarantors of the Good Friday agreement," he said.
Varadkar will also meet leaders of Northern Irish political parties, with the exception of the two main pro-British unionist parties, one of which -- the Democratic Unionist Party (DUP) -- is now in a 'confidence and supply' deal with the U.K. government.
"We will do all we can, in Brussels, in London and in Dublin, to achieve the best outcome for everyone on this island to protect our peace, our freedom, our rights and our prosperity," Varadkar said.
However, Northern Ireland's local government remains suspended. The previous administration in Belfast collapsed earlier this year with the resignation of its Sinn Fein Deputy First Minister Martin McGuinness over a botched energy saving deal in January.
Other issues about recognition of the Irish language and the legacy of violence from the 1968-1998 Troubles further soured relations between the DUP and its Irish nationalist rivals, Sinn Fein, leading to more stalemate in the divided region.
