Ten hooded assailants attacked a police station in the eastern Athens suburb of Kaisariani in the early hours of Tuesday, pelting the building with homemade firebombs.
According to the Athens-Macedonia News Agency no one was injured in the pre-dawn attack, which took place at around 4 a.m.
Police remanded five people for questioning but released them a few hours later after finding no evidence to link them to the attack.
Earlier, at around 2.30 a.m., the car of a television journalist known for covering the police's crime bulletin was blown up in the northern suburb of Papagou.
The blast was caused by a makeshift explosive device that had been placed under the woman's private car, which was parked outside her home.
There were no injuries or reports of other damage apart of that to the vehicle.
It was not clear whether the two incidents were related.