The Taoiseach Mr Ahern tonight spelt out what would be required of republicans and loyalists to resolve the difficulties in the peace process.
After a day in which he met British Prime Minister Mr Tony Blair and Ulster Unionist Party leader Mr David Trimble, Mr Ahern spoke at a debate at University College in Dublin.
He said: "While I acknowledge the very substantial contribution made by the IRA ceasefires and acts of decommissioning, the political realities are that the continued operations of paramilitary organisations, both republican and loyalist, have created a crisis of confidence which must be addressed.
"Paramilitary organisations must complete the transition to democratic and peaceful means.
"Activities, including intelligence gathering, targeting, training, arms procurement, punishment attacks and other criminal activities must end.
"The loyalist feud and the activities of loyalist paramilitaries are a cause of deep concern and recent horrific murders and punishment attacks once again underline the need for strong and effective action by the Police Service of Northern Ireland.
"I welcome the recent successes of the Police Service in taking on loyalist paramilitaries and the approach being taken by the Chief Constable, Hugh Orde."
Mr Ahern said he was confident the Northern Ireland institutions would be restored in time to allow Assembly elections to go ahead in May.
"While our approach in the period ahead should be both collective and comprehensive, it need not be lengthy," he said.
"Time is of the essence. With the necessary political will and the required intensive engagement - and from my contacts with the leaders of the pro-Agreement parties in recent weeks I believe that the necessary political will is there - I believe that it should be possible to resolve the current difficulties and restore the Northern Ireland institutions in sufficient time for the scheduled Assembly elections on May 1st, 2003.
"One thing is clear, there must be no turning back on the agenda for positive change, which the Agreement represents.
He added: "We have that opportunity in the next few months and, despite the inevitable electoral pressures and internal political constraints, need to seize it by regaining the sense of hope, optimism and courage that gave us the Good Friday Agreement in the first place."