Gardaí have said material discovered in Mountjoy jail that led to a lockdown is not firearm-related, but is believed to be a cannabis grinder.

The Irish Prison Service confirmed in a statement that a suspicious item was discovered on the C wing of Mountjoy Prison at approximately 12.30pm today.

Following an initial examination by prison staff and responding gardaí, it was suspected that the item may be part of a firearm containing a number of bullets, the statement said.

As a result, appropriate action was taken by the prison's governor and a general search of the prison was commenced.

The item was removed by An Garda Siochána for forensic examination. Gardaí have subsequently determined that the item is not part of a weapon as was initially suspected, the statement added.

The Prison Service has defended its decision to lock down the prison.