Dogu Perincek, the chairman of the small Workers Party (IP) was formally charged on Monday morning by an Istanbul court with being a high-level leader of a shadowy right wing group known as Ergenekon and having in his possession confidential documents about the state.
More than 40 people, including high ranking retired military officers, lawyers and writers, have been detained in connection with the Ergenekon case.
Prosecutors alleged that the group was planning to fan civil unrest by organising the assassination of well known public figures, including Nobel Prize winning author Orhan Pamuk. The aim of these actions was, prosecutors claim, to force the military to intervene to remove the ruling Justice and Development Party government and to restore public order.
Penincik, along with 11 others, was taken into custody in a series of pre-dawn raids on Friday morning.
Another suspect in the investigation, Professor Kemal Alemdaroglu, the former rector of Istanbul University, was released from detention by the Besktas State Security Court Monday morning.
Late on Saturday, Ilhan Selcuk, the editor-in-chief of the left leaning daily newspaper Cumhuriyet, was released after being interrogated by the public prosecutor.
However, the 83 year old Selcuk was banned from leaving the country.