Northern Ireland's politicians are being called into talks next week to resolve the crisis over IRA activity.
Taoiseach Enda Kenny and British Prime Minister David Cameron ordered negotiations to break the deadlock at Stormont as security chiefs said they would support an independent assessment of paramilitary groups.
Mr Kenny said they envisaged that the process of talks should be short, focused and intensive and deal with full implementation of the Stormont House Agreement as well as the trust and confidence issues arising from the legacy of paramilitarism.
"If the sustainability of the devolved institutions is to be ensured, it is absolutely critical that these talks are advanced with a sense of urgency and that all of the parties constructively seize this opportunity," he said.
A Downing Street statement said devolved power-sharing is facing a real threat unless there is urgent progress.
"As a result of these discussions the Government has concluded that there is a clear need to convene urgent, intensive and focused cross party talks, involving the parties engaged in the negotiations that led to the Stormont House Agreement," the statement said.
"It is vital for the sustainability of the devolved institutions that all parties seize the opportunity for urgent talks to address these issues."
Mr Kenny and Mr Cameron spoke on the phone on Wednesday and agreed the initiative.
The talks are planned for next week at Stormont House with Secretary of State Theresa Villiers representing London and Foreign Affairs Minister Charlie Flanagan, Dublin.
"The purpose of the talks is to secure full implementation of the Agreement and to deal with issues arising from the impact of continued paramilitary activity in Northern Ireland," Downing Street said.
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 Irish 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 a former IRA 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 still exists for peaceful purposes and the shooting was carried out by individual PIRA members but not sanctioned at a senior level.
The Ulster Unionist Party (UUP) last week said it could no longer work with Sinn Fein because trust has been shattered and has left the power-sharing ministerial Executive at Stormont.
Sinn Fein has said the IRA has gone away but supported calls for discussions, while the DUP called for the Assembly to be suspended for four weeks to allow for intensive talks.