Prison officers in Northern Ireland jails are taking further unofficial industrial action in a dispute over their home security.

For the second time this week, officers either phoned in sick or turned up for work and left shortly afterwards.

The head of the Prison Service, Peter Russell, said more than 90% of prison officers were involved in Friday's action.

The service said all visits were being cancelled for the day.

The protest is part of an ongoing row over security measures at officers' homes in the wake of the discovery of staff details during a police investigation into an alleged IRA spy ring.

Inmates at a wing of Magaberry jail near Lisburn refused to co-operate with prison procedures by going into their cells.

The Prison Service said that because of the industrial action by officers, the gates at the jail were temporarily sealed.

The Prison Officers' Association said some of its members were prevented from leaving the jail for a time.

Guarding prisons

On Wednesday, 600 officers failed turn up or else left the jails by reporting sick after just a couple of hours.

Police spent the night guarding Maghaberry prison in County Antrim and the jail at Magilligan in County Londonderry.

On Wednesday night, Prison Officers' Association chairman Finlay Spratt said the protest would go on.

POA members are angry at what they said was the government's failure to provide them with adequate funds to upgrade home security.

This followed the discovery of 1,400 officers' names on a list recovered during an investigation into alleged IRA intelligence gathering.

Peter Russell: "All officers are not assessed as being under the same threat"

The director general of the Prison Service said nothing would be achieved by the unofficial protest action by 85% of Northern Ireland's prison officers.

Peter Russell said there was no doubt that the 600 prison officers who either reported they were sick or came to work on Wednesday and then went home sick, were engaging in pre-planned, co-ordinated action.

It is illegal for the officers to go on strike.

Two hundred police officers were called in to work in Northern Ireland's two prisons, Maghaberry and Magilligan in Londonderry, and at the Young Offenders' Centre in Belfast.

But along with 100 prison officers who did not take part in the action, they were not able to carry out all of the duties normally undertaken.

Prisoners were not brought to court and families and solicitors were not permitted to visit prisoners.