The Northern Ireland peace process has been plunged into crisis because the Rev Ian Paisley's Democratic Unionist Party reneged on an agreement with Sinn Fein, Gerry Adams said.
The DUP had agreed to accept the devolution of policing and justice by May 2008 - the timeframe set out in the St Andrews Agreement - as long as Sinn Fein made the historic step of giving backing to the police and justice system, he said.
However a public statement never came, said Mr Adams.
The Sinn Fein president revealed that in the run up to a meeting of the party Ard Chomhairle (party executive) on December 29, the DUP had been given the text of the motion Mr Adams was putting to the meeting calling for a special party conference to ratify Sinn Fein support for policing and justice.
Mr Adams said: "They said that the required words were in the motion and that if the Ard Chomhairle accepted the motion, the DUP would respond to this in Ian Paisley's New Year statement."
He said the words given to Sinn Fein by the DUP were: "The DUP has always maintained that it will support the devolution of policing and justice if there is sufficient confidence across the community. The words needed are those contained in the Ard Chomhairle motion.
"Provided Sinn Fein translate into action the commitments contained in that motion, the DUP will accept devolution of policing and justice in the timeframe set out in the St Andrews Agreement or even before that date."
Mr Adams said that was acceptable to him and he proceeded to the Ard Chomhairle meeting. He added: "The agreed words were never said which is why there is now a crisis in the process. So the context has been changed completely.
"The DUP have refused to accept power sharing within the St Andrews timeframe. The basis of the Ard Chomhairle motion has been removed. We have to find another basis to move forward. It will be difficult but I see this as a challenge to be faced and overcome."
Dr Paisley denied giving any private assurances. He claimed Gerry Adams' statement was a diversion from what he said was the right thing to do in supporting the police, the courts and the rule of law.
