Northern Ireland's First Minister Peter Robinson has warned that Sinn Fein's failure to implement welfare reform is the problem most likely to bring down the devolved assembly.
Gerry Adams said the political process which his party leads in coalition with the Democratic Unionist Party (DUP) faces its greatest challenge since the Good Friday Agreement negotiations.
The republican leader claimed unionists had served the agenda of those opposed to the landmark peace process deal and accused the British Government of encouraging the unionist leadership by not fully engaging for four years.
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Mr Robinson said: "By far the most damaging issue that has the potential to end devolution is the shameless denial by Sinn Fein of economic realities resulting from welfare reform." Stormont deadlock over imposing welfare benefit cuts from Westminster threatens to strip millions from budgets for public spending after the Treasury threatened massive fines.
It is the latest in a series of disagreements between Sinn Fein and the DUP.
The republican party's president said there was no likelihood of talks resuming next month on contentious issues surrounding flags, parades and dealing with the legacy of thousands of conflict murders.
Mr Adams said: "The political process is in trouble."
He said there had been an absence of consistent positive leadership from unionists. The Sinn Fein president added: "The anti-Good Friday Agreement axis within unionism, the pro-unionist stance of the British Secretary of State (Theresa Villiers), the refusal of Downing Street to honour its own obligations are combining to create the most serious threat to the political institutions in the north in recent years.
"The result of all this is directly undermining power-sharing and partnership government."
But the Northern Ireland Office (NIO) has said the UK Government remains fully engaged in Northern Ireland.