British counter-terrorism officers are investigating three packages containing explosives found at three separate locations in London on Tuesday, AFP reported. According to Scotland Yard, the packages contained “small improvised explosive devices” and were found at an office block next to Heathrow Airport, the post room at Waterloo station, and at offices near London City Airport.

“The packages – all A4-sized white postal bags containing yellow jiffy bags – have been assessed by specialist officers to be small improvised explosive devices,” London’s Metropolitan Police said in a statement. “These devices, at this early stage of the investigation, appear capable of igniting an initially small fire when opened.”

The package, sent to the office near Heathrow’s north runway, burnt after being opened by staff. The Compass Centre was evacuated, the BBC reported. However, no injuries were reports and flights were not affected.

A similar package was reported at Waterloo Station in central London two hours later, but train services were not interrupted. “The package was not opened,” said the police. “Specialist officers attended and made the device safe.”

The third package found at the Royal Docks near London City Airport was also not opened and flights continued to operate as normal. “The Met Police has issued advice to transport hubs across London to be vigilant for and report suspicious packages to police,” it said, adding that they are treating the incidents as “a linked series”.

A Heathrow spokesperson said the airport would support the police investigation into the “criminal act”.

Irish police join probe

Ireland’s police service said it was assisting in the investigation as the packages were posted from the country, Reuters reported. While the Met Police confirmed it was keeping an open mind regarding motives, it declined to comment on a possible Irish link.

A picture of the envelope addressed to Waterloo appears to show its sender’s address as Bus Eireann in Dublin. Ireland’s postal service identified the stamps on the packages as its “Love & Wedding” design for greeting cards, wedding invitations and thank-you cards.