Police say they detained six terrorist suspects for questioning and recovered significant evidence from raids in three houses in the Athens area.
A police officer familiar with the case said the six suspects are being questioned but have refused to cooperate so far. The officer insisted on anonymity because he was not permitted to speak to the press.
Greek television reported that police found notes used in the preparation of proclamations by terrorist group Revolutionary Struggle as well as bomb making materials on Saturday.
Revolutionary Struggle has claimed responsibility for terrorist attacks, including the shooting of a riot policeman last year and an anti-tank rocket strike against the U.S. Embassy in 2007.
Police raided a townhouse in the northern Athens suburb of Nea Ionia and later entered another house in the town of Kalyvia, south of the Greek capital. They were searching a third house in the central district of Exarchia, known as a haven for anarchists.
Riot police were stationed near the house.
Earlier, police spokesman Athanasios Kokalakis said the investigation would continue but refused to identify the detained suspects. A prosecutor is expected to charge and name the suspects at some point during the weekend.
