LONDON — Britain's counterterrorism police are investigating after three padded mailing bags containing small explosive devices were found near major transport hubs in London.
Police said smaller bags inside the mailers enclosed the devices that "appear capable of igniting an initially small fire when opened."
Officials say the Metropolitan Police Counter Terrorism Command "is treating the incidents as a linked series."
One mailer was found near Heathrow Airport. A building was evacuated as a precaution after the package was opened and part of it burned.
Officials say the building is not at the airport and flights at Britain's busiest airport were not affected. There were no injuries.
Another mailer turned up near London's City Airport, a much smaller airport, and the third in the mail room at busy Waterloo Station, a major rail and Underground hub. Those packages were not opened.
Waterloo Station was not evacuated, but a small cordon was put in place outside the station.
Officials say train services to City Airport were suspended as a precaution but have been restored and the building where the package was found was evacuated. Flights were not affected.
Police have advised all transport stations throughout Britain to "be vigilant" and to report any suspicious packages to police.
No arrests have been made and no individual or group has claimed responsibility.
The official terrorism threat level throughout Britain is set at "severe," indicating that intelligence analysts believe an attack is highly likely.