Wires, batteries and piping which could have been used in a crude bomb have been found buried in a garden at NI's high-security prison.
No explosives were discovered during the three-day search at Maghaberry jail in County Antrim.
But prison authorities have launched an investigation after the bomb making parts were uncovered buried near the jail's perimeter wall.
A Prison Service spokesman stressed the items couldn't have made a viable bomb.
It is understood the items came from a prison workshop and a tuck shop rather than being smuggled in.
But the discovery comes less than a month after traces of a component used in Semtex explosives were found in the cells of republican prisoners during searches.
The traces were detected in swab tests taken during routine searches of two cells at Roe House.
At that time, a Prison Service spokesman said no Semtex was found during the operation.
In a statement released on Sunday, the Prison Service said: "We can confirm that some component parts of a small potential device were found in the grounds of the prison yesterday.
"The search of the prison is continuing but visits are taking place."
Maghaberry is Northern Ireland's high security prison with republican and loyalist paramilitaries among its inmates.
Prison visits resumed on Saturday following a major search.
All domestic and legal visitors had been denied access to Maghaberry prison since Thursday morning, when the search operation began.
It has been more than 10 years since the last major search at the jail.