Martin McGuinness: We're facing major crisis of our time with Brexit
Brexit is potentially bigger than the peace process for Ireland, Martin McGuinness has warned.
The Deputy First Minister said the UK decision to leave the EU was the "major crisis of our time".
Mr McGuinness was speaking at an all-island Brexit forum in Dublin yesterday.
"I've been involved in some of the most historic and important negotiations that this island has seen in 100 years, more particularly the Good Friday Agreement and the St Andrews Agreement," he said.
"What we are facing into now, in my opinion, is just as big as that - maybe even bigger."
The stark outlook is not helped by a British Government that is "all over the place" on the UK's future, he added.
Mr McGuinness said unionists - who snubbed the gathering - were shocked by the outcome of the June referendum.
He said the British opt-out had "profound implications" for the entire island of Ireland.
But he added that he was optimistic leaders in both Northern Ireland and the Republic could come together to negotiate with the British Government and the European Union.
Mr McGuinness was speaking before the All-Island Civic Dialogue, a specially-convened forum of politicians, business leaders and community representatives from both sides of the border.
Earlier, Taoiseach Enda Kenny warned that Prime Minister Theresa May could trigger Brexit within weeks.
Mr Kenny also cautioned Europe against "losing the plot" over the UK's decision.
In unscripted remarks before the conference, he said the PM had indicated she will trigger Article 50 - the mechanism for leaving - before the end of March.
"That doesn't mean it mightn't be triggered in December... or January, or February," he added.
In London, meanwhile, Mrs May pledged there will be no internal UK borders post-Brexit.
Speaking at Prime Minister's Questions in the House of Commons, she said it would not impact on inter-relations in the UK. She was responding to a question from DUP MP Nigel Dodds.
In response, Mrs May said: "I am very happy to give the right honourable gentleman that assurance in relation to movement around the United Kingdom. No change will take place.
"We will ensure that Brexit is a good deal for the whole of the United Kingdom."
Mr Dodds also referred to "dangerous" talk around the prospect of increased violence in Northern Ireland as a result of Brexit.
The PM added: "Those who wish to encourage violence off the back of that should, frankly, be ashamed of themselves.
"It is essential that we all work together to make a success of this and get the best possible opportunities for people across the whole of the United Kingdom."
Afterwards, Mr Dodds said: "This is a clear commitment from the Prime Minister, one which First Minister Arlene Foster indicated would be the case.
"There can be no question that the rights of British citizens to travel within the UK will be affected by Brexit, and I am very glad that the PM has reiterated that this is indeed the case."
Separately, Fianna Fail leader Micheal Martin attacked British Government ministers for pushing a "crude and chaotic" Brexit agenda.
Mr Martin said: "Our agenda is the clear one of wanting to minimise the damage and division of Brexit and to maximise progress for all parts of this island.
"Let's explore radical ways of softening Brexit, but we also have to talk about the crude and chaotic Brexit which some in the London Cabinet appear to be advocating.
"Unlike the Foreign Secretary (Boris Johnson), we don't have the luxury of being pro-having the cake and eating it."
Sinn Fein leader Gerry Adams repeated that his party wanted a referendum on Irish unity.