All visits to Northern Ireland's top security prison were halted yesterday as the authorities carried out a full search of the jail.
Maghaberry Prison in Co Antrim announced that all visits by relatives and lawyers were cancelled until further notice.
The lockdown was ordered by the prison's new governor Steve Rodford, who was appointed earlier this year after a major controversy was sparked by the suicide of an inmate who was supposed to be under observation.
Governor Rodford said: "Maghaberry is a high security prison. It is normal for searches to be undertaken within the prison and there are occasions when they will, unfortunately, as in this instance, lead to restrictions in the regime offered to prisoners.
"Every effort is being made to keep disruption to a minimum and I hope to be in a position to return to normal regime levels as soon as is practically possible.
"The safety and security of prisons are of paramount importance and this does require searches, both localised and extensive, to be carried out."
He added: "I have commissioned such searches in my previous career in England and see this as an integral element of managing a high security prison."
The Prison Service said it regretted any inconvenience caused and said all visits will be re-scheduled.
It said the search was in the interests of the safety of staff and prisoners.
The prison has hit the headlines over the last year.
Last month four prison medics were suspended from duty following an investigation into the suicide of an inmate.
The staff work in the medical centre at the high security Maghaberry jail where convicted sex offender John Anthony Deery was found hanging in August.
The 50-year-old died the next day in Belfast's Royal Victoria Hospital.
He was the second Maghaberry inmate to kill himself in little over 12 months.
The action against the four healthcare workers came after a probe into the circumstances of the death by the region's Prisoner Ombudsman.
Deery's death came a year after another prisoner - 34-year-old Colin Bell - hanged himself in the jail and only five weeks after a damning inspectors' report on safety standards criticised the monitoring procedures for vulnerable inmates.
Staff were disciplined after an independent probe into Bell's death discovered that wardens who were supposed to be checking the high-risk inmate were lying on beds watching TV.
New governor Steve Rodford was appointed in the wake of the episode, but had been in post for just over a month when Deery died.