Turkish media say police have detained more than 30 people in a widening investigation of an alleged attempt to overthrow the government.
The Anatolia news agency says police made the arrests Wednesday in raids across the nation.
Among those detained are retired senior military officials, a retired police chief and a pro-secular writer.
In October, prosecutors charged 86 people as part of the probe into the ultra-nationalist organization known as Ergenekon.
Those on trial include retired army officers, leftist politicians and journalists. Prosecutors accuse them of planning assassinations and bombings to sow chaos in Turkey, forcing the army to step in and overthrow the elected Islamic-rooted government.
The trial has highlighted tensions between Turkey's ruling party and the country's secular elite.
The investigation began in mid-2007 with the discovery of an arms cache in an Istanbul suburb.
Some information for this report was provided by AFP and AP.