A powerful bomb has exploded outside a maximum security prison in the west of the Greek capital, Athens.
There are unconfirmed reports that a woman was injured in the explosion, which was heard in central Athens, eight kilometres away.
The bomb was reportedly placed inside a rubbish container close to the jail wall.
A warning call was made to a Greek newspaper.
There was no immediate claim of responsibility, but correspondents say suspicion will fall on left-wing Greek militant groups, the BBC reports.
Athens has seen recent violent protests as the government unveiled tough austerity measures in return for a huge rescue package for its debt-ridden economy.