Greek police say unknown gunmen have fired shots outside the central offices of the country's Socialist PASOK party in downtown Athens, but no injuries have been reported.

It was not immediately clear whether the PASOK party offices, or the riot police guards stationed outside, were the target of the attack. The building is frequently targeted by anarchists, who pelt the entrance and riot police with petrol bombs.

A PASOK official said several dozen people were in the offices when the shots were fired, but nobody was injured.

PASOK dominated Greek politics before the country's financial crisis, but is now Greece's third-largest party, controlling 19 of parliament's 300 seats.