Four prison guards and a ‘Real IRA’ prisoner were taken to hospital today after an overnight protest at Portlaoise prison.
Prison officers in riot gear moved in to break up the protest and forcibly return up to 40 inmates to their cells on the E2 wing, a prison service spokesman said.
Those with injuries are not thought to be seriously hurt, he said.
The protest erupted after several of the men were refused temporary release yesterday.
The Republican Prisoners Welfare Association said the row centred on one particular inmate who wanted to be let out to see his sick child.
Sources said he was Damien Lawless, who is in his early 30s. He was imprisoned for three years after being caught at a ‘Real IRA’ training camp in Co Meath in October 1999.
The protest was the first major incident of its kind at Portlaoise since the 1980s, and was described as "serious" by the authorities.
A Prison Service spokesman said: "Last night a group of subversive prisoners in Portlaoise staged a protest by refusing to return to their cells.
"The protest was started when the authorities refused to grant some of them temporary release."
He added: "This morning prison staff specially equipped with control and restraint equipment forcibly moved them back to their cells."
A Garda spokesman told ireland.comthis morning no gardaí had been called in to assist prison officers overnight.
"It would have to be a very serious situation for that to happen", he said.
Ms Marian Price, chairwoman of the Republican Prisoners Welfare Association and a member of the 32 County Sovereignty Committee - the political wing of the Real IRA - attacked the "brutal" manner in which the protest was broken up.
She claimed prisoners had more serious injuries that the prison authorities had reported.