Emergency talks are under way between union, health and prison chiefs over a dissident republican threat against care staff at Maghaberry jail.
The trust responsible for health provision in Northern Ireland's prisons said its staff were "upset and distressed" by intimidating remarks made by a republican prisoners' group.
It said it was working with prison authorities to ensure the safety of workers at the Co Antrim jail. Police are investigating the comments.
Republican inmates at Roe House in the prison told health staff, including nurses and doctors, they "would do well to take note" of their concerns over what they claimed was "substandard" care.
The statement on the Republican Network for Unity website claimed that "sinister measures being taken by the jail administration" meant republican prisoners were being deprived of adequate healthcare.
A healthcare union told the Belfast Telegraph the matter was of "great concern" and the South Eastern Health and Social Care Trust said the safety of staff was paramount.
"The South Eastern Health and Social Care Trust is saddened that trust prison healthcare staff have been upset and distressed given that our staff are our greatest asset," a spokeswoman said.
"Across health and social care, people come to work every day intent on providing quality healthcare and doing a good job. It is no different in prison healthcare.
"Staff provide professional care on the basis of clinical need to those who need it. The trust values those who work in prison healthcare and the tremendous work that they do for their patients.
"The trust is very aware of the need to ensure that staff are safe and we are working with the Northern Ireland Prison Service to ensure the safety of all staff."
While the Prison Service runs the Co Antrim jail, healthcare inside is provided by the trust.
A spokeswoman for the Royal College of Nursing (RCN) in Northern Ireland said: "Any kind of threat to healthcare staff is of great concern. The RCN will continue to monitor the situation and work with the South Eastern Trust to support nurses working in this difficult environment."
Earlier this week prisoners hit out at what they claimed was a "cosy relationship" between staff from the trust and warders.
The issue is set to be raised at Stormont's health committee amid calls for the threat to be retracted immediately.Background
There are around 50 republicans being held in Maghaberry jail, Northern Ireland's only category A prison. Inmates include Harry Fitzsimons, who served two terms as a member of the Provisional IRA. He is currently on remand with two other prominent dissidents, including Lurgan republican Colin Duffy, charged with attempting to murder members of the security forces.