Police say a taxi driver was lightly injured by the blast, which occurred before dawn today during a thunderstorm.
Parked vehicles sustained minor damage, as did a sentry post outside the police station in the eastern Kaisariani district. It was unclear whether anybody in the police station noticed the explosion.
Police said the taxi driver, who was getting into his parked car at the time, did not realise what had happened until he was informed by hospital doctors that a cut in his leg had been caused by a grenade fragment.