Suspicious packages were found on Tuesday near London's major transport hubs of Heathrow Airport, Waterloo station and London City Airport, prompting Britain's counterterrorism police to launch an investigation.
The packages – all A4-sized white postal bags containing yellow Jiffy bags - have been assessed by specialist officers to be small improvised explosive devices.
These devices, at this early stage of the investigation, appear capable of igniting an initially small fire when opened, the Metropolitan Police said.
Scotland Yard's Counter Terrorism Command said it has launched an investigation.
'The Met Police Counter Terrorism Command is treating the incidents as a linked series and is keeping an open mind regarding motives,' the statement said.
The Met Police has issued advice to transport hubs across London to be vigilant for and report suspicious packages to police, after all three packages were found near major transport hubs of Heathrow Airport, Waterloo station and London City Airport.
At approximately 09:55hrs local time, the Met Police received a report of a suspicious package at the Compass Centre, Nelson Road, Hounslow, near Heathrow Airport.
The package was opened by staff at the building, causing the device to initiate.
This resulted in part of the package burning.
No one was injured and the building was evacuated as a precaution. The met Police said that specialist officers attended and made the device safe.
The building remains closed as enquiries continue. However, no flights were affected by the incident.
Then at approximately 11.40 hrs, British Transport Police were called to reports of a suspicious package in the post room at Waterloo Station. The package was not opened.
Specialist officers attended and made the device safe to ensure no one was injured.
The station was not evacuated however cordons are in place at a small area outside the station on Cab Road. Train services are continuing to operate as normal.
A third incident occurred at approximately 12.10hrs, when police were called to a report of a suspicious package at offices at City Aviation House in east London, near City Airport.
Staff were evacuated from the building as a precaution while specialist officers neutralised the package. The building has since reopened.