A letter bomb believed to have been sent by radical anarchists ignited in a Greek post sorting centre on Wednesday without causing any injuries, police said.
The police said the envelope from Thessaloniki contained a makeshift explosive device and was addressed to a senior Greek police officer, purportedly from his brother.
The bomb apparently went off by accident after the envelope was dropped by staff at a post sorting centre north of Athens, the police said.
A bomb squad team was later summoned and took out the device with a controlled explosion.
Police had initially said the envelope had come from Italy.
Similar devices had been sent by the Italian Informal Anarchist Federation (FAI) to the then justice minister and the warden of Greece's top security Korydallos prison in 2011.
FAI has expressed solidarity to jailed members of Greek militant outfit Conspiracy of Fire Nuclei, which had sent parcel bombs to European leaders and embassies and carried out arson and bomb attacks some three years ago.
Greek police suspect the latest device may have been sent in support of a Greek anarchist who has been placed in pre-trial detention alongside several Conspiracy of Fire Nuclei members, but denies involvement in the group.
The anarchist, Costas Sakkas, has been held since December 2010. He has been on hunger strike since early June to protest his innocence.