Ulster Unionist Party leader Mike Nesbitt has said Martin McGuinness’ resignation as deputy First Minister means that Sinn Féin have let the DUP off the hook.
“This is not the way to resolve the RHI scandal,” Mr Nesbitt said, following Monday’s developments.
“Sinn Féin should have stayed - to hold the First Minister to account, to force a public inquiry, and to vote on the much-needed cost controls on the scheme. Instead, they have prioritised self-interest, as always.
“This is Sinn Fein letting the DUP off the hook.”
Mr McGuinness said that he was taking the decision to tender his resignation as a result of the handling of the renewable heating incentive scheme by First Minister Arlene Foster and the DUP.
He denied that his health was a factor and further stated that Sinn Féin would not be nominating a successor to the role.
That decision would force a snap election.
But the UUP’s Mr Nesbitt said: “The public mood clearly indicates they want the facts of the RHI debacle exposed.
“To move straight to an election without this taking place is farcical.
“They had a choice between the integrity of the institutions and electoral advantage and they appear to have chosen the latter.”
He further stated: “There is a moral duty on Claire Sugden to trigger a public inquiry into the Renewable Heat Incentive before 5pm tonight.
“The public must know where the blame lies for the waste of over £400m of their money."
SDLP leader Colum Eastwood also said that Sinn Féin leaving the Executive office will give those involved in the RHI scandal a reprieve.
“It ensures no immediate consequences for Arlene Foster, no emergency legislation to cap costs and no investigation into potential corruption. Each and every day this scandal is costing taxpayers £85,000,” he said.
“If the Executive is incapable of opening itself up to accountability, I would urge the electorate to enforce their accountability at the ballot box.
“On day one of a new mandate the SDLP will guarantee our first priority will be a full public inquiry.”
The SDLP leader added that he shared the sentiments in Mr McGuinness’ resignation letter that the DUP has attacked Irish identity and culture as well as equality.
“The DUP have governed disgracefully and it has extended well beyond the leadership of Arlene Foster,” he continued.
“The nationalist community has watched this unfold year after year.
“However the nationalist community also know that Sinn Féin have been the lead players in government with the DUP for over a decade. Sinn Féin were jointly in control and are therefore jointly responsible.”
“There is a difference between being tolerant and being timid.
“For years Sinn Fein have been addicted to appeasement and are only now waking up to the reality that the DUP have been running rings around them in government."
Alliance leader Naomi Long said the DUP has "recklessly endangered" the political institutions.
"This is a head-on collision that has been building for some time," she added.
"The DUP have continued to ignore the voices who reasonably asked the First Minister to step aside voluntarily and without prejudice to allow a public inquiry into RHI, to get to the truth of this matter."
Meanwhile, Green Party leader Steven Agnew said it was a bad day for Northern Ireland.
“The Executive parties have failed miserably in their duty to get on with the job and deliver for the people of Northern Ireland,” he said.
“There is an opportunity to pull back from the brink, but the Executive parties seem unwilling to put the electorate ahead of party interests at this point in time.”
Mr Agnew added: “I do not believe that the people of Northern Ireland want an election, coming so soon after the EU referendum and 2016 Assembly election.
“However, if an election is inevitable, the Green Party is likely to improve upon our mandate, particularly given that we probed the RHI scheme tariffs as far back as 2013.”