The Government has made a "political judgment" to keep the five men jailed in connection with the killing in 1996 of Det Garda Jerry McCabe in prison, the High Court heard yesterday.
The court yesterday refused an application by two of the prisoners, Michael O'Neill and John Quinn, for early release under the Belfast Agreement.
Some 57 prisoners in the Republic and 444 in Northern Ireland have been released since 1998. The men convicted of the manslaughter of Garda McCabe in Limerick have argued that they also are entitled to release.
But a document given under the Freedom of Information Act to lawyers for one of the men said that the Government had decided against releasing them to protect support for the agreement.
It was "not a case of applying different standards in the case of persons convicted of the murder of gardaí," said the document. "Persons convicted of the murder of other gardaí, who have already served long sentences, will be covered by the prisoner release arrangements," it said.
The Sinn Fein TD, Mr Martin Ferris, said there was an onus on the Minister for Justice, Mr McDowell, to "honour commitments" under the agreement to release the men. He believed the court recognised that the men were "qualifying prisoners" under the agreement.
However, Mr Justice Peart found no individual rights were conferred of the men by the agreement. In not sanctioning their release, the Minister for Justice was exercising an executive function of a discretionary nature.
Mr Ferris said: "The Good Friday agreement committed both the British and Irish governments to releasing all qualifying prisoners within two years. That was 1998. It is now 2003."
He added: "I am conscious of the pain and upset of the McCabe family, but the Castlerea prisoners qualify under the terms of the Good Friday agreement, and there is an obligation on the government to honour their commitments and release them."
A spokesman for Mr McDowell said: "The Minister has noted that the court held in the State's favour and he will be studying the details of the judgment. As there is the possibility of further legal proceedings, the Minister will not be making any further comment."
Applications by two other men convicted in the case, Pearse McAuley and Jeremiah Sheehy, have been delayed due to disputes about discovery of documents.