As terror scares emerge both in Kenya and abroad,counter-terror police are investigating three packages containing explosives found at Heathrow Airport, London City Airport and Waterloo station.
The “small improvised explosive devices” were found in A4 postal bags, the Metropolitan Police said.
The Met’s Counter Terrorism Command is treating it as a “linked series” and “keeping an open mind regarding motives”.
No-one has been hurt, the force added.
The Compass Centre in Heathrow’s grounds was evacuated after a package was reported to police at about 09:55 GMT.
The device set alight when staff opened the bag, the Met said.
A Heathrow spokeswoman said the airport would assist the police investigation into the “criminal act”.