Unofficial protest action by prison officers is causing significant disruption, the Northern Ireland Prison Service has said.

Up to 85% of officers either phoned in sick on Wednesday or turned up for work and then reported sick.

Police officers have been drafted in to the prisons to provide cover while the protest continues.

A Prison Service spokesman said they had not been informed of any planned industrial action.

Finlay Spratt: Prison officers feel frustrated

All visits to Maghaberry and Magilligan prisons and Hydebank Young Offenders' Centre were suspended for the day.

Lawyers scheduled to make visits were turned away from Magilligan Prison.

It was understood the Prison Service had contingency plans in place following rumours that a protest involving sick leave would take place.

The action is linked to ongoing prison officers' protests over alleged security breaches by the IRA.

It follows a police investigation into IRA intelligence gathering, in which the personal details of officers were found on a laptop computer.

A special police unit was set up to warn those whose names appeared on the list seized.

Meanwhile, the director general of the Prison Service, Peter Russell has defended the time taken to tell prison officers if they are under threat.

"It's a question of how quickly we can get around the numbers of staff.

"We've been doing our best to reschedule days of attendance and release staff from duties to go to the briefing meetings," he said.

'Officers frustrated'

Prison Officers Association chairman Finlay Spratt said its members wanted prison management and the government to properly compensate officers forced to move home to protect themselves.

"Something like this happening would be unofficial and would be the decision of the prison officers themselves," he said.

"You can understand the frustration the prison officers are going through and the stress that their families are going through over how they've been treated by the Northern Ireland Office."

In recent weeks, the staff at Maghaberry and Magilligan prisons and the Young Offenders' Centre at Hydebank have staged one-hour protests.

The Democratic Unionist Party's Ian Paisley Junior said he had already warned the secretary of state about the consequences of mass sick leave in the prisons.

Lawyers have been turned away from Magilligan Prison

"It is a potential security disaster," he said.

"The government had better waken up to the reality that if they don't address this issue quickly and expeditiously, prison officers will bring the Prison Service to a complete and utter halt," he said.

Last week, the association said prison officers were considering industrial action if they did not get more compensation for increasing security at their homes.

The Prison Officers' Association said they feared almost 1,500 names, addresses and telephone numbers of serving officers may be on the list.

In a statement the Northern Ireland Prison Service said the prison officers' case "would only be progressed with the good will and co-operation of all parties".

The government has a number of programmes in place, including the Assisted Home Removal Scheme, to help with the costs of moving those in Northern Ireland under threat.

A second programme for those wishing to remain in their present home meets the costs of installing security measures.