The accusations that have been denied by Russia have been levelled by several Italian newspapers. Italy's Corriere della Sera reports that tests carried out by the German security service came up trumps. The tests show that the memory sticks and chargers could be used to snoop around in computers and telephone data.
Diplomatic sources in Brussels are reportedly awaiting the outcome of further tests before launching a protest.
It is unclear whether any members of international delegations actually used the gadgets.