The Conspiracy of the Cells of Fire claimed responsibility on Sunday for planting a car bomb that blew up a vehicle that belonged to the governor on Korydallos Prison.
The explosion happened during the early hours of Friday, leading to one person suffering minor injuries and nearby vehicles and homes being damaged.
Authorities said the device contained up to 1.5 kilos of high explosives.
In its statement, which was published on the Internet, the group warned of an imminent “storm.”
The group has been active since 2008 and was linked to a number of bloodless bomb attacks targeting public figures as well as a series of letter bombs sent to embassies and foreign governments in 2010.
Two suspected members of the group were arrested earlier this month. Four people were convicted of being members of the group last October