A Prison Service spokesman said officers suffered smoke inhalation after four fires at Maghaberry Prison in Lisburn, County Antrim, on Sunday.

"Fires have been a feature of Maghaberry for the past 12 months"

There had also been two fires on New Year's Eve, he said.

Another officer was treated for minor burns on Sunday after a prisoner threw tea over him.

It is understood that prisoners started fires in cells and recreational areas in protest at being locked in their cells for longer than normal because of high levels of staff sickness.

The Prison Service said restrictions had to be imposed because 150 of the jail's 820 officers are off sick.

It was suspected that the high level of sickness was "a symptom of low morale" among staff, he said, adding that the prison service was aware of the problem and was looking at ways of tackling it.

'Lack of resources'

More than 1,000 prison officers are to lose their jobs because of a huge cut in the prison population over the next two years due to the Good Friday Agreement early release scheme, and the expected closure of the Maze prison.

The first few hundred jobs are set to go in the spring following more than 200 early releases.

Finlay Spratt of the Prison Officers Association said the problems the jail were not new.

"These fires have been a feature of Maghaberry for the last 12 months - it all comes down to a lack of resources," he said.

"They don't have enough staff on duty to provide a normal regime so the prisoners end up having to be locked up and unfortunately when this happens the prisoners react.