A major investigation was under way at the Republic's top security jail in Portlaoise last night after rampaging INLA prisoners attacked the governor and several officers.

Some of the dissident republicans hurled the contents of their chamber pots in the direction of Governor Ned Whelan and a number of his staff.

Prison officials said last night that Mr Whelan had been splashed by the contents but was not injured in the incident.

Tensions had been rising in the wing of the prison housing renegade republicans for the past couple of days.

Last Saturday staff learned that an INLA member had created a home-made weapon out of the handle of a soup ladle, staff said.

A search of a cell on E4, the landing housing the eight INLA prisoners, including the organisation's alleged leader in Dublin, Declan Duffy, was carried out by prison officers on Sunday morning.

The INLA inmates objected to the search and were then alleged to have poured the contents of their pots through the mesh netting, which leads to the E3 landing holding 21 Continuity IRA prisoners and the E2 landing housing 30 Real IRA inmates.

Some of the content seeped into an area housing food and a kitchenette in the Real IRA area and this was immediately shut down, pending an examination.

Members of the INLA also apologised to the Real IRA over the seepage incident.

On Monday the INLA group lodged complaints that their cells were being unfairly targeted for searches and protested that they were being selected for special treatment.

Their protests continued throughout the day and yesterday morning staff took two of the INLA men out of their cells and brought them to the segregation unit.

Governor Whelan was attacked shortly before noon as he was making his regular rounds of the jail and stopped at the INLA landing to tell the inmates that their accusations were unfounded.

While addressing the inmates he came under fire from the pots and extra staff were drafted onto the landing to restore order. However, according to staff sources last night, five of the INLA men managed to make their way through the wire netting and reached the landing occupied by the Continuity IRA inmates, who supported their protest.

Sources said staff were very concerned as the inmates could have gained access to weapons such as pool cues and balls, weights from the gym and items from the craft shop.

But following talks with senior management in the afternoon the inmates eventually returned to their cells without further disturbance.

The Irish Prison Service said last night that the group had been involved in a minor disturbance, which had been quickly brought under control.

But staff sources said it was the first time that a prison governor had been attacked by inmates in Portlaoise in over 30 years.

The Prison Service said the incidents were being fully investigated. It was learned later that the five INLA prisoners involved in the incident had been punished last night by being locked up in their own cells for more than a month without access to phone calls or visits.