Suspicious packages were found Tuesday near Waterloo Station, London City Airport and Heathrow Airport, UK counter-terror police said.

The “small improvised explosive devices” were discovered in postal bags, the Metropolitan Police said.

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

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The Metropolitan Police Counter Terrorism Command is investigating the incident.

“We’re treating the incidents as a linked series & keeping an open mind regarding motives. Flights at Heathrow & City Airport have not been affected. Train services at Waterloo Station continue to operate. As a precaution, some DLR services were suspended but now fully operational,” police said in a tweet.

Authorities said they received a call after one of the packages was opened at the Compass Centre by an employee, “causing the device to initiate” and partially light on fire. Later, police received a call of another package at the post room at Waterloo Station.

Police in Ireland are reportedly assisting London's Metropolitan Police with the investigation after the three devices had distinctive Irish post stamps on them, according to Sky News.

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Police said no one was injured in the incident.