The mystery fifth letter bomb sent by a group calling itself the IRA is believed to have been finally located at a sorting office in Limerick.

A group calling itself the IRA claimed responsibility for sinister parcels sent to major transport hubs in London and a university in Glasgow earlier this month, one of which burst into flames when it was opened.

The organisation, known to police as the New IRA, claimed one parcel, addressed to a British army recruitment officer, may not have been discovered yet.

The group claimed it posted five devices to addresses in Britain, but only four had been discovered at the time the claim of responsibility was sent to a Belfast newsroom.

Defence minister Charlie Flanagan said a stamp on the package found in a postal sorting office in Limerick had a similar stamp to those letter bombs sent to the UK.

"This is a despicable act," he told RTE. "The sending of incendiary devices like this is totally unacceptable. I hope the people responsible are brought to justice."

Mr Flanagan said the item found in Limerick could be the fifth, adding: "We have reason to believe this could be the case."

A Garda spokesman said: "Shortly after 6am, Gardai in Henry Street received a report of a suspect package at the An Post sorting office, Dock Road, Co Limerick.