Sinn Fein TD for Kerry North Mr Martin Ferris has called for the release of the Provisional IRA members charged over the killing of Det Garda Jerry McCabe in Adare, Co Limerick, in 1996.
Four are serving terms for manslaughter and the fifth on a related conspiracy charge over the killing. They are being held in Castlerea low-security prison in Co Roscommon.
On Thursday, the High Court refused an application by two of the prisoners, Michael O'Neill and John Quinn, for early release under the Belfast Agreement.
"The Minister for Justice and the Government must realise there is an obligation on them to implement the Good Friday agreement and that includes the release of the 'Castlerea Five'," Mr Ferris told his party's ardfheis in Dublin today.
He criticised the Minister for Foreign Affairs Mr Cowen for saying that most of the main issues at stake in the North's peace process had been resolved.
"If they were resolved, we would clearly not be in the current predicament," he said.
Mr Ferris also called on the British government to speed up the process of demilitarisation. "We will not be satisfied with anything less that a timetable to dismantle the British war machine in the six counties," he added.
A motion from a Belfast branch stressing concern atgrass-roots levels about the lack of information from the party leadership on talks between the Irish and British governments was passed by delegates.
At least 2,000 Sinn Fein members were expected to attend the ardfheis in the RDS, Ballsbridge. The event - which is being broadcast live on RTE - began yesterday and concludes tomorrow. Party president Mr Gerry Adams is due to address the ardfheis at 5 p.m. this evening.
