A bomb has exploded at the offices of Golden Dawn, a neo-Nazi group based in Greece.
The device caused "a lot of damage" to the offices, based in Aspropygos, near Athens, but there were no injuries or fatalities.
A police official said the explosion, which took place before dawn Monday, was a "powerful blast".
The bomb was homemade and packed with dynamite. It blew out the windows of several nearby stores, caused significant damage to a ground-level shop and to the offices of the far-right group, which are based on the first floor.
Golden Dawn has an extreme nationalist agenda and advocates ridding Greece of all immigrants.
It rose to prominence during recent elections, with the country in a deep economic crisis. The party won 18 seats in the 300-member parliament during the elections in June.
Golden Dawn has been the subject of fierce criticism and repeated controversy over recent months. It is accused of demanding a list of all foreign children attending kindergarten schools and daycare in Greece, and pressurising local businesses to sack foreign workers and replace them with Greek nationals.
Last week the party came under further scrutiny after a demonstration in Crete, during which one MP threatened to kill anti-fascist protesters and another unfurled the flag of the 1967-1974 military junta - a series of right-wing military governments that ruled Greece.