Stormont First Minister Peter Robinson today said there will be "no further" meetings of the power-sharing executive until the political crisis over the IRA is resolved.
The DUP had unsuccessfully sought a four-week adjournment after police said members of the Provisional movement shot former IRA man Kevin McGuigan dead in east Belfast last month.
The DUP had promised it would not be business as usual when Assembly members returned from their summer break today. Intensive talks launched by the British and Dublin governments are due to begin later this week.
Mr Robinson said: "Pending a satisfactory resolution of the outstanding issues, business will not be as usual. As a first step there will be no further meetings of the Northern Ireland Executive unless we deem that there are exceptional circumstances.
"In addition, there will be no North/South ministerial meetings in any of its formats (between ministers in Belfast and Dublin).
"Our ministers shall be focused on the talks process."
Branding the Assembly "not fit for purpose" Mr Robinson said the DUP would continue to push for an adjournment but his ministers would take part in Question Time "on this occasion".
He added: "In my view the Assembly is not fit for purpose as it stands today.
"Leaving aside the issue of the Kevin McGuigan murder it still wasn't fit for purpose. So, those issues have to be resolved.
"Unless those issues are resolved we will not have a functioning Assembly and we made it very clear without a resolution to these matters in the talks process our ministers' resignations will follow."
The DUP has been accused of playing "hokey cokey" over its decision to halt all but exceptional Executive meetings at Stormont.
Standing over his decision to pull out of the five-party coalition, UUP leader Mike Nesbitt said the DUP was sending out mixed messages.
"I think they are being a little bit more confused. I think it is a bit of hokey cokey they are playing," he said.
"We at least were a bit more definite. We said business would not be as usual. This is the first day in the history of parliament in Northern Ireland that an Assembly has been in session without an Ulster Unionist Party in government."
Although the UUP would embrace the forthcoming talks process, Sinn Fein and the police must be on the "same page" with regards to the status of the IRA, Mr Nesbitt said.
He added: "That has to be resolved as a matter of urgency.
"I expect Sinn Fein and the PSNI to end up on the same page. I expect them to work hard to end up on the same page."
Politicians are due to debate a Sinn Fein motion condemning the murders of former IRA members Jock Davison and Kevin McGuigan, and calling on anyone with information to pass it on to the police.
Police have insisted the IRA is not back on a war footing but the disclosure that the organisation still exists has rocked an already badly-divided political establishment.
The British government has decided to legislate on welfare reform if the Stormont parties cannot reach agreement.
The DUP and Sinn Fein have been at loggerheads over the issue for months and the devolved administration in Belfast has been plunged into financial peril.
Sinn Fein Newry and Armagh Assembly member Conor Murphy said it would be a grave mistake for the British government to return welfare powers to Westminster.
"There are no doubts in relation to our view in terms of the British government deciding in an arbitrary fashion to take powers back off the Assembly.
"Martin McGuinness has said very clearly that would be unacceptable to us and he has said very clearly that would be a grave mistake."
The Ulster Unionists have left the power-sharing Executive because they claim they cannot trust republicans following the murder of Mr McGuigan.
Mr Murphy said the party would not be distracted by an electoral contest within unionism.
"We are mandated to be here to do business, we are mandated to fight austerity and the impact of Tory cuts on frontline public services and on vulnerable people.
"We are also mandated to negotiate if negotiations arise and that is what we intend to do. We intend to deliver on that mandate, it is up to others to explain, I suppose, what the effect their actions will have on our ability collectively to deliver for communities and to deliver for people who elected us all to this institution, to work this institution.
"We are not threatening the institution, we are here to do business, we are not going to allow ourselves to be distracted and we intend to continue with that business."
Talks are planned for this week at Stormont House with Secretary of State Theresa Villiers representing London and Foreign Affairs Minister Charlie Flanagan, Dublin.
The purpose is to secure full implementation of the Agreement and to deal with issues arising from the impact of continued paramilitary activity, Downing Street has said.
Mr Robinson said: "If we are not satisfied that the parties are applying themselves to achieving an outcome in a reasonable timeframe we will initiate a further step or further steps. If it becomes apparent to us that a satisfactory resolution in the talks is not possible then as a last resort ministerial resignations will follow.
"However, we must make it clear that any election which follows such an eventuality will not be an election to return to the present Assembly arrangements as we will not nominate a First Minister until a fundamental and more wide-ranging negotiation produces a system that can fully function."
The move came after the PSNI offered a new assessment of Provisional IRA activity stating that aspects of the terror organisation have gone away, its active service units do not exist any more and what remains fulfils a radically different purpose than during the Troubles.
Both the Dublin government and the DUP support a new form of paramilitary monitoring of the ceasefires.
The breakdown in relations at Stormont reached a new low after the killing of former IRA member father-of-nine Kevin McGuigan, allegedly by former terror associates.
That murder earlier this summer caused political uproar after PSNI chief constable George Hamilton said the IRA - which was supposed to have gone away a decade ago - still exists for peaceful purposes and the shooting was carried out by individual PIRA members but not sanctioned at a senior level.
