A former Turkish military chief is being held in jail, accused of leading a terror organisation and conspiring to bring down the government, his lawyer said.
He is the most senior officer to face trial in a series of investigations into alleged anti-government plots.
General Ilker Basbug was arrested and kept in a prison near Istanbul overnight after seven hours of questioning by prosecutors investigating allegations that the military funded dozens of websites aimed at discrediting the Islamic-rooted government of Prime Minister Recep Tayyip Erdogan in 2009.
Some of the suspects already charged in the case, including senior generals and admirals, have said they acted in a chain of command. Basbug, who retired in August 2010, led the military at the time.
The jailing of a former military chief - unimaginable a few years back - comes as the government, which has won three successive elections, has sharply reduced the political clout of the military. Military leaders have staged three coups and forced an Islamist prime minister to quit in 1997.
Basbug's lawyer, Ilkay Sezer said his client has denied accusations during questioning. NTV television said the former general told court officials the charges were "tragicomical".
The alleged conspiracy was first reported by a Turkish newspaper in 2009, which printed a photocopy of an alleged plan to damage the reputation of the government by portraying it as corrupt.
Investigations into the reported conspiracy were inconclusive because the original document, allegedly signed by a navy colonel, could not be found. The probe was revived last year after an unidentified military officer allegedly sent the original document to Istanbul's chief prosecutor.
Hundreds of people, including civilians, retired generals and active-duty officers, are already on trial accused of terrorism charges for alleged involvement in separate plots that prosecutors say were aimed at destabilising Turkey and bringing the government down. The military says 58 serving generals or admirals are in jail.
Erdogan's opponents see the trials as a government effort to intimidate them through the courts.