SDLP 'has turned its back on the Good Friday Agreement'
Gerry Adams has attacked the SDLP and Ulster Unionists for going into Opposition.
The Sinn Fein president said the parties had a duty to inform voters of their intentions during the Assembly election.
He added: "We will work to achieve the partnership the people want.
"The SDLP and the UUP have chosen to go into Opposition. They should have told the people that during the election.
"These were the two lead parties in government for nine years and they made a mess of it. The political institutions were suspended twice and crashed twice."
Sinn Fein also accused its nationalist rival of abandoning the Good Friday Agreement.
Conor Murphy, widely regarded as a potential replacement for Deputy First Minister Martin McGuinness when he retires, said: "By walking away from the Executive it is clear the SDLP has abandoned its responsibility to the electorate.
"On the back of yet another poor election, the SDLP has now turned its back on the Good Friday Agreement.
"Their excuse that they did not understand the Programme for Government process is both dishonest and contradicted by their engagement in that process since December."
SDLP MLA Claire Hanna retorted by saying it would not take any lessons from Sinn Fein, which she claimed had walked away from negotiations on forming an administration in the Republic recently.
SDLP leader Colum Eastwood also won backing for the move from former deputy leader Brid Rodgers, who said the party had not acted against the legacy of John Hume, one of the chief architects of the Good Friday Agreement.
"The vision of John Hume, the aspiration of John Hume, for a real partnership and power-sharing Executive that would heal the divisions of the past and help us to grow together has not happened, particularly in the last nine years," she said.
"There hasn't been real partnership in the last nine years. It has been a carve-up."
The row came as speculation mounted a DUP MLA could become Justice Minister, or that the two main parties would share the portfolio rejected by Alliance.
First Minister Arlene Foster and Mr McGuinness insisted the appointment of ministers will go ahead next Wednesday.
DUP leader Mrs Foster has ruled out a Sinn Fein MLA taking on the role of Justice Minister, but Mr Adams yesterday refused to be drawn on whether republicans would accept a DUP politician in the post.
Speaking in west Belfast, he said: "Over the last two mandates the SDLP and UUP have agreed to all the Programmes for Government, implemented them, but then refused to play any constructive role.
"We have to have a full Executive elected on Wednesday. If we don't, then we are into another election, so we are looking at options to make sure it is elected. I'm not going to discuss (the possibility of a DUP Justice Minister) at this time."
Alliance refused to take on the role, which leader David Ford held for six years, after the DUP and Sinn Fein rejected a series of demands from the party, including restrictions on the Assembly's controversial petition of concern mechanism, which the Big Two have used to block legislation.
Alliance has also refused to join the Opposition.
Instead, its eight MLAs will bolster the ranks of Stormont's 'naughty corner' alongside Jim Allister, the Greens and People Before Profit.
A party spokesman said: "We do not actually technically qualify for Opposition in any case. The legislation says any party must have 8% of the vote to be included in an Opposition, and we fall just shy at 7.8%."
Sinn Fein has made clear on several occasion that its preferred option would be for Alliance to retake control of the Department of Justice.