Senior security sources have warned tensions are threatening to boil over among dissident republicans at Northern Ireland's high-security prison.
There are fears over the situation at Maghaberry in Co Antrim amid claims the prison authorities are at risk of losing control of the dissident wing in Roe House.
An influx of republican suspects and convicted terrorists is said to be putting staff under huge strain.
The chair of Stormont's justice committee told the Belfast Telegraph the situation was at "breaking point" and warned he feared the lives of prison staff were at risk.
And the head of the Prison Officers' Association said the service was under severe pressure, with sick levels due to stress soaring.
"There's no doubt there's tension within Roe House as a result of the ongoing campaign by dissident republicans," Paul Givan, head of the justice committee, said.
"It's the numbers and the type of republican being detained who are very much trying to pressurise and force the issue of their demands and get more control.
"There are significant personnel forcing the issue who have been there, served their time, and are back in. So the pressure has increased since some of those senior republicans returned to Roe House.
"There's no doubt they are trying to get more control over their particular landings and that's something which causes the prison officers concern over their own safety.
"There's already a view within those officers that there's already too much control." There are 50 separated republican prisoners currently detained at Roe House within Maghaberry – including high-profile terror suspects Colin Duffy and Thomas Mellon.
A Department of Justice spokeswoman said: "We do not comment on operational matters such as the relationship between staff and prisoners."
DUP MLA Mr Givan urged Justice Minister David Ford to scrap an agreement struck with republican prisoners in August 2010.
Some prisoners went on a dirty protest in 2012, claiming that the prison authorities reneged on a deal brokered at that time to end a policy of routine full body searches, replacing it with electronic scanners.
The prisoners claimed the deal was that they would be searched using a BOSS (body orifice security scanner) chair.
Prison authorities said the agreement was for internal movement within the prison only, not when prisoners left and re-entered their wings for domestic and legal visits or trips to court.
Tensions over the same issues have ratcheted up in recent weeks, it is claimed.
"Prison officers are still under threat, that is a real threat which is there," said Mr Givan. "Ultimately, the fear is that people's lives could be lost as a result.
"David Black lost his life recently over what is going on at Maghaberry and there is a fear you could be facing another incident because of this campaign."
So concerned by the situation, Sinn Fein sent a delegation to Maghaberry last month headed up by MLA Raymond McCartney, a former IRA prisoner and hunger striker.
Afterwards, the party said it "raised our concerns over controlled movement, visits and how these have a negative impact on a regime which should be based on dignity and respect".
But a statement issued on behalf of dissident republicans inmates of Maghaberry's Roe 4 was scathing of Sinn Fein.
They said it was "a pathetic and sorry rejection of just how far these people have gone in propping up both the prison regime and the unionist stalemate we once resisted together".
The group added: "Prisoners will resist all attempts to criminalise us whether through controlled movement, strip-searching or isolation."
A protest on behalf of republican prisoners is due to take place on the Falls Road this Saturday.
Father-of-two Mr Black was murdered on the M1 in 2012 as he drove from his Cookstown home to Maghaberry.
Earlier this year letter-bombs were sent to named members of staff at the jail.
Prison Officers' Association head Finlay Spratt claimed staffing levels at prisons meant one warden can often be tasked with overseeing 25 prisoners.
"We are seeing one member of staff over 25 or two over 50 prisoners," he said. "It used to be eight to 50 prisoners. It's ridiculous."
Those behind bars
THOMAS MELLON: The taxi driver is accused of directing a dissident republican terror group.
In June the High Court refused bail to Mellon after describing a note he is alleged to have written as displaying "a chilling disregard for human life".
Mellon, of Rathmore Road in Londonderry, was arrested after the letter, believed to have been smuggled into Maghaberry Prison, was seized.
The 38-year-old father-of-four denies charges of directing terrorism and membership of a proscribed organisation.
The note, written on joined up pieces of cigarette paper and wrapped in cling film, was taken from a visitor to the jail. The court heard it contained a communication to members of the so-called New IRA being held in custody.
COLIN DUFFY: Colin Duffy is being detained at Maghaberry having been charged with conspiracy to murder and IRA membership.
Two other men were separately charged in connection with a murder bid on a police patrol in north Belfast, when shots were fired at officers at a sectarian interface.
The three alleged dissident republicans were covertly recorded seeking out security force targets with a high chance of "getting a kill", the High Court heard in July.
GAVIN COYLE: Gavin Coyle (36), from Omagh, who admitted possessing a large cache of guns and explosives, was sentenced to 10 years earlier this year. He was arrested in 2011 when detectives investigating the murder of policeman Ronan Kerr discovered the arms dump in a garage in Coalisland.
Items seized included Semtex explosive; four AK47 assault rifles; ammunition and magazines; a booster for an RPG rocket; three bomb timer units; a number of electronic incendiary devices; components of an improvised PRIG grenade, explosive powder and detonating cord. Last year Coyle, from Culmore Park, admitted possession of explosives and firearms with intent to endanger life and membership of a proscribed organisation.
GUN GANG: Four men caught with a loaded gun in their car in Omagh in 2010 were given jail terms this year.
Mark McGuigan, of Sperrin View, Omagh, was sentenced to 12 years; Daniel John Turnbull, of Strule Park, Omagh, to nine years; Martin McLoone, of Abercorn Road in Derry, to eight years, and Darryn Patrick McCallion, of Rathlin Drive, also Derry, to seven years.
The following day police carried out a search and found a Renault Clio car belonging to Turnbull. Inside, officers found a sub-machine-gun and magazine along with 42 .22 calibre cartridges.
Police also uncovered three sets of ballistic body armour, latex gloves, ear defenders and combat clothing during the 2010 operation.
BRENDAN McCONVILLE AND JOHN PAUL WOOTTON: Earlier this year two dissident republicans lost an appeal against their convictions for murdering a police officer.
Brendan McConville and John Paul Wootton will serve their respective jail terms for the killing of Constable Stephen Carroll – the first member of the PSNI to be murdered.
Constable Carroll was shot by the Continuity IRA in an ambush in Craigavon, Co Armagh, in March 2009. The 48-year-old from Banbridge, Co Down, was targeted as he sat in an unmarked police car while colleagues responded to a 999 call.
In 2012 McConville (43), from Craigavon, and 23-year-old Wootton, from Lurgan, were found guilty at Belfast Crown Court of Constable Carroll's murder.
They were also convicted of possession of an AK47 assault rifle and a quantity of cartridges with intent to endanger life.
TERROR TRAINING CAMP: In June three men and a woman admitted charges over a dissident republican training camp in Co Tyrone.
It was found at Fourmil Wood, on the outskirts of Omagh, in March 2012.
Sharon Rafferty (38), from Cabhan Aluinn, Pomeroy; Sean Kelly (48), from Duneane Crescent, in Toomebridge; and brothers Aidan Coney (35), from Malabhui Road, Carrickmore, and Gavin Joseph Coney (36), from Gorticashel Road, Omagh, will be sentenced on the charges at a later date.