Counter-terrorism officers are “keeping an open mind” in the hunt for those responsible for sending explosives to three transport hubs in London.
Devices were found in A4 postal bags at London City Airport, Heathrow Airport and Waterloo Station on Tuesday.
Irish police are assisting with the investigation as Republic of Ireland stamps were on at least two packages.
British Transport Police said it had more officers on the transport network to provide “reassurance”.
Both airports and Waterloo station are running as normal, with London City Airport saying there would be a “visible police presence” in the area.
Met Police Deputy Commissioner Sir Stephen House said the investigation was in its “very early days”.
Speaking at a London Assembly police and crime committee meeting, he said advice had been issued to London’s transport hubs to be “more vigilant than they normally are” for suspicious packages.
If you’re flying through London City today, let us know on here where you’re off to. Yesterday’s incident did not affect flights and passengers should continue with their travel plans as normal. As ever, our staff are on hand, alongside a visible @metpoliceuk presence.
— London City Airport (@LondonCityAir) March 6, 2019
Nobody was injured by the “small improvised explosive devices”, which were found in white postal bags containing yellow Jiffy bags.
The first package caught fire when it was opened by staff at Heathrow’s Compass Centre at about 09:55 GMT.
The other two were discovered over the next three hours.
