The Provisionals had been linked to the raid which saw two employees’ families held hostage, because similar tactics to the multi-million pound Northern Bank heist were used.
Republican involvement would destroy any lingering hopes of restoring Northern Ireland’s power-sharing regime, unionists warned.
But while police have yet to blame anyone, it is understood an IRA operation is not a major line of inquiry.
Police may instead be scouring the underworld networks for possible clues to the crime gang behind this carefully planned theft.
The store reopened yesterday after forensic teams examined the premises on Donegall Place.
While two families were held captive at their homes in the south and west of the city overnight, the staff members were ordered to go into work on Saturday and clear out all cash.
The money was put in sports bags and given to gang members at a nearby branch of Alliance and Leicester Building society.
The handover, in front of early morning shoppers, took place just yards from the scene of the December raid on the Northern Bank when £26.5m was seized.
In that robbery, which shattered attempts by London and Dublin to put together a new deal to revive the Stormont Executive, hostages were also taken while employees brought the cash to waiting thieves.
Democratic Unionist MP Sammy Wilson warned: “It looks like the finger is again pointing at the IRA and if that’s the case it will have very serious implications. It would simply reinforce what we have been saying, that they have no intention of giving up criminality.”
Belfast’s Deputy Lord Mayor, Pat Convery said: “This was a chilling and cowardly robbery. Families are traumatised and businesses damaged.”