The power sharing institutions at Stormont risk becoming valueless, a leading member of Sinn Féin has warned.

The party has called repeatedly for DUP First Minister Arlene Foster to stand aside while an investigation is carried out into a massively overspent green energy incentive which left taxpayers facing a potential £490 million bill over the next 20 years.

Speaking on RTÉ's News at One, the party's national chairperson Declan Kearney said if Ms Foster does not step aside, pending a preliminary report into the scheme, his party would look at all options.

These options include fresh elections, less than a year after the last vote.

Mr Kearney said the DUP was in denial over the RHI controversy, adding that the crisis was deepening as the credibility of political institutions was being damaged.

Sinn Féin is due to take the matter to the devolved Assembly later this month in what could be a crucial date for the future of the administration it jointly leads with the Democratic Unionists.

Earlier, Mr Kearney said: "Political institutions cease to have value when they do not reflect equality, mutual respect and parity of esteem, and have become detached from the lives of citizens they are meant to serve."

Ms Foster became leader of the DUP and First Minister just over a year ago and produced success in last year's Assembly elections, emerging triumphant as Northern Ireland's largest party.

In a previous role as economy minister she established the Renewable Heat Incentive scheme which paid business owners more in subsidies than the fuel cost and led to a "cash for ash" scandal.

Claims of widespread abuse include a farmer allegedly set to pocket around £1 million in the next 20 years for heating an empty shed.

Mr Kearney added: "Political parties and leaders in the north need to be above scandal and corruption. They should be above reproach, not continuously reproachful towards political opponents.

"The political process has now been dragged recklessly by the DUP, culminating with the RHI crisis towards an unprecedented tipping point."

He added: "Playing fast and loose with the political process and the political institutions is unsustainable.

"There are big decisions to make, and there is very little time."

Ms Foster has repeatedly blamed her officials for the debacle.

In a letter to Northern Ireland's leading banks written at the outset of the ill-fated scheme, Ms Foster said the state-funded eco-subsidies offered applicants a "good return on investment".

Following Mr Kearney's comments the SDLP has called on Sinn Féin to back its call for an independent, judge-led inquiry into the RHI scandal.

Mid Ulster MLA Patsy McGlone made the call amid what he called contradictory positions from Sinn Féin on their plan to achieve transparency and accountability on the issue.

The SDLP member said: "Surrendering the demand for a judge-led public inquiry is surrendering the need for transparency, accountability and consequences for the loss of hundreds of millions in public money.

"With trust in our hard-won institutions at stake, Sinn Féin need to think very carefully on where their loyalties lie.

"The SDLP have been clear, only a judge-led inquiry can get to the truth of this matter. Sinn Féin must return to this position immediately."