British counterterror police say they are investigating three packages containing "small improvised explosive devices" found in separate locations in London.
The devices were found in A4-sized postal bags at Heathrow Airport, London City Airport, and Waterloo train station, police said on March 5.
The devices "appear capable of igniting an initially small fire when opened," they said.
The Metropolitan Police’s Counterterrorism Command is treating the incidents as a "linked series" and "keeping an open mind regarding motives".
No one has been hurt, the force also said, and no flights or trains are believed to have been affected by the incidents.
Ireland's police said they were helping their British colleagues investigate as at least two of the packages had Republic of Ireland stamps.
The device found at Heathrow Airport ignited when staff opened the bag.
The two other suspicious packages were not opened and have since been "made safe," according to police.