Two inmates at HMP Kilmarnock have tested positive for Covid-19.
The Scottish Prison Service (SPS) confirmed the cases on Thursday and said another 28 people at the jail are “symptomatic”.
Both individuals who have tested positive are being cared for within the SPS estate and have not required hospital treatment.
Those showing symptoms are self-isolating within their cell for seven days.
An SPS spokeswoman said: “We can confirm that two prisoners within HMP Kilmarnock have tested positive for Covid-19.
“We are working closely with Health Protection Scotland and NHS colleagues to support those in our care and are following their advice.
“Clinically-led protocols for the management and care of those who contract Covid-19 are in place and advice and guidance about steps which should be taken to prevent the spread of Covid-19 have already been issued to staff and those in our care.
“At this time there are no restrictions on movement in place therefore establishments are continuing to operate visits as normal.
“Anyone within our care who is presenting with symptoms of Covid-19 is required to self-isolate within their cell for seven days.
“Those who are self-isolating still have access to food and medication and we are working on ways to maintain communication with friends and family.”
It comes as the number of cases across Scotland rose to 266, with 12 of those in the NHS Ayrshire and Arran region.
Prison services union Community criticised the jail, saying it is “unacceptable that there is still free prisoner movement” inside.
Regional secretary Steve Farrell said: “There should be restricted movement and a controlled unlock – this is in the interests of both the officers on the front-line and the health of the other prisoners.
“We all understand that we are dealing with a challenging situation and we have committed to working constructively with the prison contractors to get through this.
“However, we are not going to remain silent when our members’ health and safety could be compromised when there are operational choices that could be taken, which would go towards addressing the problem.
“In light of the unprecedented circumstances, the independent prison director should have the autonomy to take appropriate steps to ensure the safety and well-being of our members, without fear of any financial penalties being imposed by the Scottish Prison Service.”