Rome police defuse bomb on politician's car
The street was blocked off and experts defused what news reports described as a rudimentary device.
"A very serious event, I express my full solidarity."
Doria had already been under police protection for prior threats, according to reports.
Television channel TGcom24 said the threats related to his denunciation of illegal squatting in historic buildings, and damage to statues and fountains.
Rome prosecutors have opened an investigation.