Police in Monaco and neighboring France were hunting for a man suspected of detonating a makeshift bomb in the center of the Mediterranean principality on Monday and wounding several people, a local official said.
Two of the victims suffered life-threatening injuries, Christophe Mirmand, minister of state of Monaco, told BFM TV.
French emergency services deployed to the scene to provide backup, and a joint police operation was underway to track down the fugitive, France's interior ministry said.
"No event of this nature has ever happened in the Principality before," Mirmand told the French news channel.
The blast occurred shortly before 9 p.m. local time in the center of Monaco, a tax-free microstate on the French Riviera known as a haven for billionaires and their luxury yachts.
French newspaper Le Figaro said video surveillance images showed a man dropping a backpack at the entrance of a residential building shortly before the explosion.
The attack is 'a tragedy for Monaco'
BFM TV described the explosive device as a "parcel bomb," citing the principality's prosecutor general.
Eric Ciotti, the right-wing mayor of nearby Nice, across the border in France, said on X: "The attack committed this evening is a tragedy for Monaco."