Two retired generals were jailed in connection with an alleged plot to topple Turkey's Islamic-rooted government, the highest-ranking ex-soldiers detained as part of the probe, a news report said.
The two, arrested late Saturday, were among 21 people rounded up in the past week in the investigation into an alleged pro-secular and nationalist network called "Ergenekon," the state-run Anatolia news agency said.
Ret. Gen. Hursit Tolon, who once headed the paramilitary force, and former top army commander Sener Eruygur, who helped organize a series of anti-government rallies last year, were being held at an Istanbul jail Sunday.
No charges have been filed, and details about the alleged plot were sketchy Sunday. Some newspapers close to the government have said the suspects were plotting a series of events - such as mass demonstrations and violent clashes with police - that would lay the ground for an army takeover.