A blast from an explosive device wounded Ukrainian oligarch Vadym Yermolaiev and two others in Monaco on Monday, authorities said, in a “deliberate” act unprecedented in the principality.

Three people including a teenager were wounded in the explosion that struck around 9pm local time in a residential building on a street along the border with France.

A source close to the investigation who asked not to be named said that one of those wounded was Yermolaiev.

Monaco’s Minister of State Christophe Mirmand initially said the blast appeared to be “an attack”, but later dropped that term, describing it as a “deliberate explosion”.

Monaco’s Prince Albert II described the incident as a “heinous crime” and “a shock to the entire Monegasque community”.

An aide to France’s Interior Minister Laurent Nunez said police were working “to find the perpetrator, who has fled”.