Poll: Do you support idea of joint authority for Northern Ireland?
- There can be no British-only direct rule, for NI, insists Dublin
- London hits back, saying there will never be joint authority
Westminster is furious after the Irish Government said it should be involved in the running of Northern Ireland if talks to restore Stormont fail.
And the DUP suggested that should Dublin be granted a greater say, the unionist party would bring down Theresa May's government, which relies on its MPs' votes in Parliament.
Irish foreign affairs minister Simon Coveney stepped into controversy after saying that direct rule from London cannot be imposed in Northern Ireland without Irish input.
With little likelihood of a return to Stormont soon, and relations already strained by Brexit and the border, Dublin appears to have hardened its stance.
"There can be no British-only direct rule," Mr Coveney said. "That is the Irish Government's position."
The Good Friday Agreement bestowed a legal obligation on the Irish Government over North/South issues affecting Northern Ireland and the Republic.
Mr Coveney said: "It would be very difficult to even contemplate how direct rule would function in that context.
"We don't want to go there, it is not good for Northern Ireland, it is not good from the point of view of the government that I am a part of, it is not good from the point of view of the government in London, everybody loses in that scenario."
However, the suggestion that any form of joint authority could be on the way met a massive backlash in Belfast and London.
A spokesperson for the Government insisted joint authority would "never" happen, and both Westminster and Dublin were committed to restoring Stormont.
"Should this not prove possible, in the absence of devolved government, it is ultimately for the UK Government to provide the certainty over delivery of public services and good governance in Northern Ireland, as part of the United Kingdom," they said. "This is consistent with our obligations under the Belfast Agreement.
"We will never countenance any arrangement, such as Joint Authority, inconsistent with the principle of consent in the Agreement."
DUP MP Sir Jeffrey Donaldson said there would be repercussions for Theresa May's government if Dublin was given a say on the internal affairs of Northern Ireland.
"If that were to happen it would have grave consequences for the stability of the government at Westminster and for the prospect of restoring devolution in Northern Ireland," he said.
The Lagan Valley MP said his party is "very clear that in the event of direct rule, it will be direct rule from Westminster and there's no absolutely no question of any form of joint authority with Dublin".
"The Irish Government would know that such a move would be a fundamental breach of all of the agreements that we have entered into.
"Even if we have a temporary period of direct rule, the Irish Government must be clear that it must not interfere with the internal affairs of Northern Ireland and to do so would be a fundamental breach of faith.
"In those circumstances I think it could damage the agreements we have reached and make it much more difficult to reinstate devolution."
Dublin is under a legal obligation to be consulted on issues involving North/South co-operation under the 1998 Agreement.
But Sir Jeffrey said: "The North South Ministerial Council does not operate outside devolution."
He added that while London and Dublin would continue to co-operate on matters of mutual interest "there can be no question of Dublin interfering with our internal affairs".
Ulster Unionist leader Robin Swann MLA said the Republic's claims to Northern Ireland in Articles 2 and 3 of its constitution were gone "and the Irish Government should remember that".
"If this is indeed something being seriously contemplated, then it goes without saying that it categorically does not have the support of the UUP," he said.
"Such a scenario makes the restoration of a fully functioning Stormont all the more imperative."