Shots have been fired at the Athens headquarters of Greece's ruling New Democracy party, but nobody was hurt.
No party officials were there when the attack happened early on Monday.
A bullet landed in an office sometimes used by the conservative Prime Minister, Antonis Samaras.
A government spokesman said left-wing anarchist groups were suspected. In recent days three of the party's offices have been attacked. Small bombs have been placed at journalists' homes.
At least one Kalashnikov assault rifle was used in Monday's attack and nine bullet cases were found. The spokesman said there appeared to be two assailants involved.
The bullets hit Mr Samaras' office at the party headquarters - though he normally works from a different building in central Athens.
The spate of attacks comes after police recently raided a large squat, arresting many anarchists inside and confiscating petrol bombs and other material, the BBC's Mark Lowen reports from Athens.
A group calling itself Militant Minority said it was behind the attacks on the houses of the journalists who were, it claimed, "official representatives of the system".
The government spokesman called the attacks an "easy way to make an impression" by groups who were "breathing their last gasp".
- 11 January 2013
- 18 May