The move came as the Irish Prime Minister, Bertie Ahern, prepared to travel to Belfast tomorrow in a renewed drive to settle the row over the IRA's refusal to give up its arms.
Unionists are insisting there must be some IRA decommissioning before the new Northern Ireland Executive and North-South ministerial councils can be formally established.
The original deadline for decommissioning to begin passed yesterday without a breakthrough. Sinn Fein and the IRA have been under sustained pressure in recent weeks from within the nationalist camp to begin decommissioning by disposing of its Semtex.
The four released from Portlaoise Prison included three of the IRA's top bomb-makers.
They are Gabriel Cleary, 54, of Tallaght, John Conaty, 37, from Ballymun and Bryan McNally, 56, from Foxrock, south Dublin, who all received 20 year terms in 1996 for arms and explosives offences.
They were caught when police raided one of the largest IRA bomb factories ever discovered, in a concealed underground bunker on a farm at Clonaslee, County Laois in June 1996. They were not due to be released until 2011.
The raid uncovered a huge cache of weapons, from mortar tubes to Semtex, and large quantities of nitrate and ammonia used in home-made explosive. Guns, timers and mortar parts were also found.
The fourth man freed was Denis Lahiffe from Dartry, sentenced last year to a nine-year term for possession of detonating cord.
Their release brings to 22 the number of convicted terrorists freed in the Irish Republic since the signing of the Good Friday Agreement.Reuse content