The residence of Greece's President Katerina Sakellaropoulou, was targeted by supporters of convicted terrorist Dimitris Koufodinas on Tuesday afternoon.
The group threw flyers in support of the hunger-striking prisoner and shouted slogans before departing. None of them were detained.
Stressing that "Democracy is neither terrorised nor blackmailed", government spokesman Christos Tarantilis condemned the attack.
63-year-old Dimitris Koufodinas is serving 11 life sentences for murder, armed robbery and use of firearms and explosives as a leading member of the militant group November 17, whose members remained at large for decades until a botched bomb attack in 2002.
He argues that his transfer in December to a high-security prison in central Greece was illegal and is demanding to return to the Athens prison where he had spent most of his sentence so far.
Moreover on Monday evening, 5 individuals also vandalised the offices of Action24 sports TV station.
They sprayed slogans relating to Koufodinas’ case and threw rocks, damaging the glass-front entrance. Police detained one person so far.
Deputy Prime Minister Thodoris Livanios condemned the attack with a post on Twitter: "Every attack against news media is an attack against Democracy".