Mountjoy prison was last night on lockdown as hostage negotiators tried to resolve a hostage situation in a basement cell where five prisoners were threatening the life of another inmate with homemade weapons in an apparent row over conditions.

At 5.30pm yesterday evening, the five inmates in cell number two in the B basement took a prisoner hostage after he defecated in the cell, according to sources.

The five inmates held homemade "shives," weapons made from plastic and other sharp materials, to the prisoner's throat and stomach during the incident.

As a result, Mountjoy was last night on lockdown, meaning that no other inmates were allowed out of their cells and prison service negotiators were brought in to try and resolve the situation. At 8.30pm last night the situation was on-going.

The ringleader of the group is said to have "flipped out" when the prisoner defecated in the cell and is protesting about overcrowding, prison conditions, as well as visitation rights in the jail. The six are being held in a four-man cell.

"We're always concerned about riots and other problems in the summer; it's always the time of year when things seem to explode," said a spokesman for the Prison Officers Association (POA). "Where the incident is happening is in the same basement where Gary Douch was murdered in 2006."

The inmate who is being held hostage is understood to be serving a 12-month sentence. "They are threatening to kill him. We don't know how serious they are. Time will tell. Overcrowding at Mountjoy is at a dangerous level," added the spokesman.

Prison management and staff were on standby last night to deal with the situation, which sources described as "volatile".

In July 2006, Gary Douch (21) was beaten to death by Stephen Egan (25), from Coolock, a psychotically ill inmate who was left without his medication for three days and then attacked Douch. "After what happened to poor Gary Douch, we were told nothing like that could happen again. But three years on exactly, we have another dangerous situation in the same basement," said the source.