Self-styled anarchists lobbed homemade firebombs at a riot police unit stationed near the Athens Polytechnic.
The incident, which took place around 2 a.m. on Wednesday, was followed about half-hour later by an attack on a riot police detachment near the headquarters of socialist PASOK party on Harilaou Trikoupi Street in Exarchia.
There were no reports of arrests or injuries.
It is not known if the attacks were related to a police operation earlier this week to evict asylum seekers from occupied buildings in the downtown Athens neighborhood, an anarchist stronghold.
A total of 134 asylum seekers were evicted on Monday. The squats were boarded up on Tuesday but police remain on guard amid fears that anarchists will try to reoccupy them.