Sinn Féin has insisted that an independent investigation into a botched renewable heat scheme cannot go ahead unless First Minister Arlene Foster steps aside.
Minister Michelle O'Neill reiterated the party's demand for the under pressure DUP leader to stand down as she outlined proposed terms of reference for an independent panel investigation into the Renewable Heat Incentive (RHI) scheme.
She said the key element of their plan is the need to be able to compel witnesses and subpoena documents related to an initiative that has left Stormont facing a £490 million overspend bill.
"If they can't compel people in papers then the investigation is not going to be worth the paper it is written on," Ms O'Neill said.
She added: "Arlene Foster needs to stand aside to allow the issue of public confidence to be dealt with. We need to have a full transparent independent investigation."
"For us, this is clearly an issue of public confidence. We have to deal with that and we will continue to deal with that. If Arlene Foster wants to do the right thing, the right thing to do is to stand aside."
Relations between Sinn Féin and DUP have deteriorated further after 'clear the air' talks collapsed yesterday.
Finance minister Máirtín Ó Muilleoir emerged from a meeting accusing economy minister Simon Hamilton of proposing a "sticking plaster" rather than a long-term plan to curb the cost of the botched green energy scheme.
The botched energy sheme has left the taxpayer facing a £500 million bill due to a failure to cap subsidies.
The state-funded RHI scheme was supposed to offer a proportion of the cost businesses had to pay to run eco-friendly boilers, but the subsidy tariffs were set too high, and without a cap, so it ended up paying out significantly more than the price of fuel.
This enabled applicants to "burn to earn" - getting free heat and making a profit as they did it.
Claims of widespread abuse include a farmer allegedly set to pocket around £1 million in the next two decades for heating an empty shed.
Mrs O'Neill said there was no agreement with the DUP on the Sinn Fein proposal.
"There is a scandal here that is going to see the drip feed of £490 million out of the public purse - that's an issue we need to get to the bottom of," she said.
"At the heart of our terms of reference is the issue of compellability. Any investigation has to have the powers to be able to compel people and papers to come before it."
She added: "Also at the heart of the terms of reference we have talked about the need for Arlene Foster to stand aside, they have obviously clearly set out their stall in relation to that not going to happen - so there is no agreement with the DUP in relation to these terms of reference."
The scandal has erupted at a time when Sinn Fein Deputy First Minister Martin McGuinness has been experiencing health problems.
Mrs O'Neill said her party colleague remained at the "core" of the party's response to the RHI affair.
All rival parties at Stormont have demanded Mrs Foster stand aside while her role in the affair is investigated.
Mrs Foster oversaw the inception of the RHI scheme during her time as economy minister.
She has steadfastly refused to step aside and has claimed some of those calling for her head are motivated by misogyny.
Senior members of Sinn Fein have warned they will exercise their power to collapse the Executive if Mrs Foster does not temporarily stand down to facilitate a probe.
If the republican party follows through with that threat Northern Ireland will be facing a snap Assembly election, less than a year after the last one.
Earlier Stormont's independent justice minister accused Northern Ireland's political leaders of letting her down over their handling of a botched renewable energy scheme.
Claire Sugden said she favoured an independent probe into an initiative that has left Stormont with a £490 million bill but said she did not support calls for First Minister Arlene Foster to step down while that investigation takes place.
Ms Sugden also ruled out quitting her pivotal job - a move that would likely force the collapse of the Democratic Unionist/Sinn Fein led coalition.
The power-sharing executive cannot function without a justice minister and Ms Sugden was the only Assembly member both DUP leader Mrs Foster and Sinn Fein Deputy First Minister Martin McGuinness could agree on in the wake of last year's election.
"Martin and Arlene have both let me down," she said.
The Justice Minister added: "Arlene and Martin might have reneged on their responsibilities to actually do a job for the people of Northern Ireland but I am not going to do that because I do have integrity and I will keep doing it until I can't."
The state-funded renewable heat incentive (RHI) was supposed to offer a proportion of the cost businesses had to pay to run eco-friendly boilers, but the subsidy tariffs were set too high, and without a cap, so it ended up paying out significantly more than the price of fuel.
This enabled applicants to "burn to earn" - getting free heat and making a profit as they did it.
Claims of widespread abuse include a farmer allegedly set to pocket around £1 million in the next two decades for heating an empty shed.
The Justice Minister had not commented publicly on the RHI scandal for over two weeks - prompting criticism from political rivals.
Breaking her recent silence, Ms Sugden said her job had become increasingly difficult.
But she said she would not resign because she still felt she could help change people's lives for the better in her role. She also stressed that her quitting would send the Executive down a "path of no return".
In an interview with BBC Radio Ulster, the minister added: "I think with this particular issue there is a lot of political posturing going on. Regrettably the two main parties are reverting to party politics and they are feathering their own nests in that respect - they are keeping their own constituents right."
Ms Sugden said she did not believe calls for Mrs Foster to stand aside were fair.
"Anyone forcing her to step aside is actually punishing her for something that hasn't been substantiated," she said.
Ulster Unionist leader Mike Nesbitt and Alliance Party leader Naomi Long have said Northern Ireland Attorney General John Larkin should not be asked to appoint the chair.
Mr Nesbitt said that as Mr Larkin had been appointed by the First and Deputy First Ministers, somebody not accountable to them should appoint the chair. He suggested that person should be Northern Ireland's Lord Chief Justice, Sir Declan Morgan.
Mrs Long said it would not be appropriate for the Attorney General to appoint the chair.
"The Attorney General is a barrister, not a judge. He can't appoint anyone senior to him. He is not in charge of the judiciary," she said.
Mrs Long added that she could not understand why Sinn Fein "cannot bring themselves to call for a full public inquiry".
Ulster Unionist leader Mike Nesbitt said he believes that Sinn Fein and the DUP have "run out of road" and that he is ready for an election should the political institutions collapse.
He dismissed Sinn Fein's proposals for an independent investigation into the RHI scandal as a "red herring" and insisted that First Minister Arlene Foster must resign.
"In terms of restoring public confidence in the integrity of these institutions, Arlene Foster should lead honourably and the only honourable thing to do is resign," said Mr Nesbitt.
He added: "It's very difficult to see how we work our way around this now because we have the two parties of government in a stand-off and I don't see what the solution is.
"If we are going to an election we are ready for it, we will look forward to it. We do believe this is a different scandal from the others of the past 10 years. People understand it and they are angry about it. Therefore there's a real prospect that for once people might, in significant numbers, vote for change."
