Police are investigating the suspected connections to two terrorist groups of a 29-year-old man arrested over the weekend in connection with a letter bomb attack in May on former prime minister Lucas Papademos and other similar attempted hits.
The man, who was named by police on Monday as Constantinos Giagtzoglou, had been under investigation for two months.
He was caught in the early hours of Saturday leaving an apartment block near central Athens with several bags containing guns, explosives and eight fake police identity cards.
The 29-year-old is believed to have close ties to the Conspiracy of the Cells of Fire, which claimed responsibility for sending a letter bomb to Berlin in March for the attention of then German Finance Minister Wolfgang Schaeuble.
That package was intercepted before it could go off but another bomb, sent to the offices of the International Monetary Fund in Paris, detonated, injuring a secretary.
Police are also probing possible links between the suspect and another guerrilla group, Revolutionary Struggle, a leading member of which was arrested in January. Panagiota Roupa joined her partner, the group's leader Nikos Maziotis, in prison.
Police feared that the 29-year-old had been planning another attack, probably on behalf of the Conspiracy of the Cells of Fire.