Martin McGuinness has said there is an overwhelming desire in the Northern Ireland community for Arlene Foster to step aside amid a growing political crisis over a green energy scheme scandal.
In a New Year's Day message, the Deputy First Minister said the First Minister and her Democratic Unionist Party needed to accept widespread demand for a thorough investigation into the Renewable Heat Incentive (RHI) scheme.
"There is also no doubt that we are facing a serious growing political crisis in the North as public confidence in the political institutions has been grievously undermined by the RHI debacle and the DUP's failure to deal responsibly and adequately with it," he said.
"In order to address these challenges, the DUP and its leader Arlene Foster need to accept there is an overwhelming desire in the community to deal with this issue and for Arlene Foster to step aside as First Minister pending a preliminary report."
The Sinn Féin chief said Ms Foster's stepping aside would allow for an investigation led by an independent judicial figure from outside Northern Ireland and appointed by the Attorney General.
"A rigorous process to recoup as much of the money as possible must also be put in place," he added.
We need to restore public confidence in the credibility of the political institutions, ensuring they deliver for the people.
Mr McGuinness's repeated demand for his power-sharing partner in the Executive to step aside follows the publication of a letter Ms Foster sent to bankers about the RHI when she was economy minister in January 2013.
In it, she said payments made under the scheme would be "guaranteed".
She also told the region's leading banks that the state-funded eco-subsidies, set up by her as economy minister, offered applicants a "good return on investment".
The revelations have raised further concern over her claim that half of the estimated £490m (€575m) public money overspend could be clawed back.
The scheme offered businesses subsidies to run eco-friendly boilers, but the tariffs were set too high and, unlike the same scheme in Britain, there was no cap.
This allowed 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 £1m in the next two decades for heating an empty shed.
Stormont economy minister and fellow Democratic Unionist Simon Hamilton has defended his party leader in recent days after a wave of calls for her to step aside.
He accused opposition MLAs attacking Ms Foster of offering nothing more than "party political attacks and resignation calls".
"On the one hand they call for a process to establish the facts but they have already decided what the outcome should be," he said.