A time bomb exploded outside the Athens home of a Greek prison director overnight on Friday, smashing windows and slightly injuring one woman in the face, police officials said.
The device, which police estimate contained at least 1 kg of dynamite, was left under a car used by Maria Stefi, director of the high-security Korydallos prison, in the Dafni neighborhood.
Police cordoned off the area after an unidentified caller warned Greek news website zougla.gr that a bomb would blow up in 20 minutes. The device went off at about 0140 GMT and one woman was slightly injured in her home by broken glass.
"We believe this is an act of domestic terrorism," said a police official who spoke on condition of anonymity.
No one has claimed responsibility for the explosion.
Small homemade bomb attacks by militant groups are frequent in Greece and usually target police, public buildings or businesses.
Attacks on political figures and journalists have picked up in recent months, some claimed by anti-establishment leftists angry about Greece's financial woes.
In January, two Greek anarchist groups claimed responsibility for an explosion at an Athens shopping center that fueled fears of rising political violence.