MONACO — An explosion in a residential building in Monaco on Monday evening injured three people. Authorities are searching for a man suspected of detonating a makeshift bomb.

The blast occurred at approximately 9:00 pm local time in a residential building situated along Monaco's border with France. Video surveillance images showed a man dropping a backpack at the entrance of the building shortly before the explosion.

Police are investigating the incident and stated that the suspect fled the scene on foot towards the French border. Monaco public prosecutor general Thibault Stéphane said a suspect had left a bag or package in the building's lobby before the explosion. Stéphane said two of the victims were in critical condition.

Monaco's Minister of State, Christophe Mirmand, stated that a couple in their 50s or 60s sustained life-threatening injuries. He added that a 13-year-old who was "very likely related to the couple" suffered less serious injuries. Mirmand did not disclose the nationality of the victims, though Le Figaro reported the victims were Ukrainian.

Mirmand described the blast at the residential building as "very likely an attack." The explosive device reportedly contained bolts and buckshot, he said. BFM TV characterized the device as a "parcel bomb," citing the principality's prosecutor general. Mirmand also stated, "This is the first time in history, to my knowledge, that such an act has taken place in the principality." Stéphane said nothing appeared for the moment to indicate why the building may have been targeted. Éric Ciotti, Mayor of Nice, said, "The attack committed this evening is a tragedy for Monaco."