Detectives investigating devices sent to addresses in London and Glasgow have said a claim of responsibility has been made in the name of the “IRA”.
The Met and Police Scotland said similar packages were sent in the past by dissident Northern Ireland groups.
Officers also revealed that one package may be unaccounted for.
The devices arrived on 5 and 6 March at Waterloo Station, buildings near Heathrow Airport and London City Airport and the University of Glasgow.
A joint statement from Police Scotland and the Metropolitan Police said the claim of “IRA” responsibility was received on Monday by the Belfast-based Irish News. A recognised codeword was used.
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