The IRA has claimed responsibility for explosive devices found at three buildings in London and Glasgow last week, London’s Metropolitan police said.
The claim was received on Monday by a media outlet in Northern Ireland and contained a recognised codeword used by the group.
In a statement, the Met said the caller had described how five devices had been sent, although only four have so far been found.
“Given the packages received last week bore similarities to devices sent in the past which were linked to dissident groups associated with Northern Ireland-related terrorism, officers were already looking at this as a line of enquiry. However, we continue to keep an open mind and enquiries continue,” the statement read.
Detectives from the Met Police’s terror unit were called in following the delivery of the suspect packages at Waterloo station, Heathrow airport and London City airport on 5 March.
Another was found at the University of Glasgow which was then evacuated.
The parcels were white postal sacks containing small A4-sized Jiffy bags.
Ireland’s main police force confirmed at the time it was assisting the Met with its investigation after pictures broadcast by Sky News appeared to show Irish stamps attached to the packages.
One of the devices was opened by staff at a building opposite Heathrow, causing it to detonate before 10am. The package caught fire but nobody was injured, police said.
The Irish Republican Army (IRA) has fought under various forms throughout the 20th century for an Ireland free from British rule.
The group was responsible for a number of attacks during The Troubles in the 1970s and 80s, including the Omagh bombing in 1998 which killed 29 people.