A suspicious package sent to a university in Glasgow is believed to be linked to the three 'love bomb' letters sent to transport hubs in London.
Several buildings at the University of Glasgow were evacuated yesterday and a controlled explosion was carried out.
Police later confirmed there were "similarities in the package, its markings and the type of device" to the incidents in London.
Results of forensic tests on the three parcels found in London transport hubs are being studied by gardai.
They hope fingerprint and DNA checks on the A4-sized packages and Jiffy bags will yield some clues.
Although dissident republican faction the New IRA remains the prime suspect for the heart-stamped "love bombs", the Met's senior counter-terrorism co-ordinator, Dean Haydon, acknowledged it had found nothing yet to indicate the motivation of the sender.
Mr Haydon Scotland Yard was pursuing a number of lines of inquiry, including the Irish stamps and postmarks on the packages, but pointed out there were no messages contained within them.
Senior gardai said it was unusual that, 24 hours on, no one had claimed responsibility, if the devices were the work of dissident republicans.
"In the past, some group would claim responsibility, or at least jump on the bandwagon after a similar incident, but nobody has yet come forward," one officer said.
The New IRA was responsible for seven parcel bombs sent to British military recruitment centres across the south-east of England, including Oxford, Brighton, Canterbury, Slough, Aldershot, Reading and Chatham, in February 2014.
The latest devices, sent to Heathrow and London City airports and Waterloo Station, were described as small with "some degree of sophistication".
One of the devices caught fire when the package was opened but no one was injured.
Meanwhile, Tanaiste Simon Coveney said he reacted with a combination of embarrassment and anger when he heard that the packages had been posted from here. He told independent.ie's Floating Voter podcast that whoever sent the packages, which had Dublin postmarks, should be "isolated and criticised".
"I think any decent thinking person needs to reject utterly the kind of warped thinking that results in somebody sending an explosive device or something that can catch fire in the post into anywhere," he added.
He said the Government would intensify contingency plans for the Border if MPs at Westminster voted for a no-deal Brexit next week.
He said his reaction was "one of bemusement as to why anyone would want to send even a small explosive device like this".
"The fact that it could happen and come from Dublin is something I and many other people would be uncomfortable with," he added.