Turkey's former army chief was arrested on Friday over an alleged plot to topple the government of Turkish Prime Minister Recep Tayyip Erdogan.
General Ilker Basbug's lawyer said authorities have jailed his client, who is accused of leading a terrorist organization.
A Turkish prosecutor called for the general to be taken into custody on Thursday after he was named as a suspect in an alleged Internet campaign aimed at destabilizing Erdogan's Islamic-based government.
Turkish media reports said earlier this week that Basbug was called to answer questions in connection with the trial of current and former officers linked to the so-called secularist network, Ergenekon.
Turkish authorities have detained more than 300 people including journalists, academics and politicians as part of a wide-reaching investigation into Ergenekon.
The case has highlighted international concerns about press freedom in Turkey.
Thursday, journalists Nedim Sener and Ahmet Sik were among 13 defendants who appeared in court to begin their defense case against charges they are linked to Ergenekon. Sener told reporters the real reason he is on trial is because he wrote a book criticizing the government.
Prosecutors say the group plotted in 2003 to bring down the government through bombings and other attacks to discredit the government and trigger a military coup against the ruling Justice and Development Party. Turkey's military ousted four governments between 1960 and 1997.