"An Garda Siochana continue to liaise with the UK Authorities in relation to these investigations".
Staff at the main sorting office on the Dock Road, alerted Gardai after coming across the package shortly after 6am.
"This parcel appears to be identical to parcels. discovered earlier this month in London and Glasgow", a police spokesman said.
He said that the incident was "a awful effect of the uncertainty surrounding Brexit where in the context of the heightened tensions in Northern Ireland, on the island of Ireland, people have taken it upon themselves to send letter bombs - an absolutely despicable act".
A letter bomb found at a postal depot in Co Limerick yesterday is identical to the devices sent to England and Scotland, gardaí have said.
Flanagan said the sending of letter bombs was "totally unacceptable" and linked it to heightened tensions in the British province of Northern Ireland around Britain's exit from the European Union.
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A group calling itself the IRA has claimed responsibility for parcel bombs sent to major transport hubs in London and the University of Glasgow.
Mr Flanagan said the item found in Limerick could be the fifth, adding: "We have reason to believe this could be the case".
The sorting depot was evacuated early this morning with around 100 staff being sent home for the day.
A viable improvised explosive device in a plastic envelope was identified and made safe.
Police believe it's linked to a number of similar devices sent to locations in the United Kingdom earlier this month.
The "IRA" said it was responsible for placing a vehicle bomb which detonated outside a courthouse in Londonderry in January.