In an early morning gun assault in January, attackers opened fire on the building near the centre of Athens with a Kalashnikov rifle. A bullet pierced a window in Prime Minister Antonis Samarass office but no one was hurt. 

The Peoples Fighter Group posted its claim online on Wednesday, saying its original plan to fire a rocket-propelled grenade had failed. 

We promise the struggling Greek people that next time we will be more efficient, the militant group said in the statement. 

It called Greece a colony of the Troika - the IMF, the European Central Bank and the European Commission - which has agreed to bail out Greeces crisis-hit economy in return for reforms and cuts. 

The Peoples Fighter Group did not explain why it had taken so long to claim responsibility. 

Police officials said they believed the online report was credible. 

The gun assault followed a spate of makeshift bomb attacks against journalists and political figures, some claimed by leftist groups angry about Greeces deep financial crisis. 

Greece is in the sixth year of a deep recession that has fuelled anger against foreign lenders and the political class, blamed by Greeks for bringing the country close to bankruptcy.