Counter terrorism police are investigating whether Russian spies planted a bomb in a parcel that caught fire at a delivery warehouse after arriving on a plane to Britain.
Fire crews and staff tackled the blaze on July 22 at the DHL warehouse in Minworth, near Birmingham.
No-one is thought to have been injured in the incident first reported by The Guardian and German broadcasters.
The package – said to contain an incendiary device – is believed to have arrived at the DHL warehouse by air but further details about the plane and its flight path are unknown.
A similar incident reportedly took place in Germany in the same month and investigators are looking at links between the two.
A Counter Terrorism Policing spokeswoman said: “We can confirm that officers from Counter Terrorism Policing are investigating an incident at a commercial premises in Midpoint Way, Minworth.
“On Monday, 22 July, a package at the location caught alight. It was dealt with by staff and the local fire brigade at the time and there were no reports of any injuries or significant damage caused.
“Due to the circumstances, and the specialist capability and expertise in investigating such matters, the investigation is being led by officers from the Met’s Counter Terrorism Command with support from colleagues from Counter Terrorism Policing West Midlands.
“The investigation remains ongoing and there have been no arrests in our investigation at this time. As part of our inquiries, officers are liaising with other European law enforcement partners to identify whether this may or may not be connected to any other similar-type incidents across Europe.”
It comes after MI5 boss Ken McCallum last week warned Russia is intent on causing “mayhem” on UK streets.
The security agency’s director general said Britain should “expect to see continued acts of aggression here at home” from Russia, with its military intelligence agency the GRU on “sustained missions”, adding: “We’ve seen arson, sabotage and more.”
Moscow’s embassy in London disputed Mr McCallum’s statement, describing it as “unsubstantiated” and claiming Russia itself was “the real target of proxy and mercenary warfare as well as hostile intelligence operations” conducted by the UK and its Nato allies.
DHL said it is taking steps to “secure its network, staff and assets as well as customer shipments by implementing strengthened security measures across the European countries as a reaction to ongoing investigations by authorities from several countries.”
