Police in Monaco and France were searching for a suspected bomber on Tuesday after three people were wounded by an explosion in the wealthy principality, which two sources said was an attack on a Ukrainian-born oligarch.

Two of the victims suffered life-threatening injuries, police said. One of the wounded is Ukrainian oligarch Vadym Yermolaiev, a source said.

Three people including a teenager have been wounded in an explosion at a residential building in Monaco, which authorities described as a "deliberate" act.