Russia could be plotting to plant bombs on passenger and cargo jets heading to the US, security officials in Europe say.
Incendiary devices found being shipped across Europe could be a test for a covert Russian operation to start fires on planes flying to the States.
Investigators have discovered at least two such devices after fires at DHL shipping hubs in Leipzig, Germany and Birmingham, Britain.
Poland’s national prosecutor’s office said four people had been arrested in connection with the fires.
They have been charged with participating in sabotage or terrorist operations on behalf a foreign intelligence agency.
“The group’s goal was also to test the transfer channel for such parcels, which were ultimately to be sent to the United States of America and Canada,” the prosecutor’s office said.
It made no reference to which foreign government was behind the covert operations. However, Pawel Szota, the head of Poland’s foreign intelligence agency, said Russia was to blame.
The secretive weapons were found to be electronic massagers modified with a flammable magnesium-based substance, according to a report by the Wall Street Journal.
Western sources have previously told The Telegraph that these items are being shipped to Germany and Britain from Poland and Lithuania.