British counter-terrorism police have launched an investigation after three “small explosive devices” were found Tuesday at three major transport hubs in London. Authorities received separate reports of suspicious packages at London’s Heathrow Airport, the Waterloo train station, and the 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,” the Met Police Counter Terrorism Command said in a statement on Tuesday. “These devices, at this early stage of the investigation, appear capable of igniting an initially small fire when opened.” There have been no arrests at this time and no one has been reported injured, police said.

Images reveal the devices were placed in white plastic postage bags with handwritten addresses. The packages were reportedly sent from Dublin, and the Garda, Ireland’s police force, is now assisting the London police in their investigation. London Mayor Sadiq Khan thanked police for their “swift actions” in locating the trio of devices. “Our thanks go to police, security, transport staff and all involved for their swift actions to keep our city safe,” he said.