Prosecutors say the plotters operate inside the "deep state"
More than 30 people have been detained in Turkey in a widening inquiry into an alleged coup plot.
Those arrested reportedly included three retired generals and a former police chief.
Some 86 people are already accused of an ultra-nationalist plot to stoke unrest that would provoke the army to launch a coup.
Critics say the ruling AK Party is simply arresting some of its most prominent secular opponents.
Wednesday's police operation involved simultaneous raids in six provinces, the Turkish state news agency Anatolia said.
A court in Istanbul also ordered searches of the suspects' homes and workplaces, it said.
A larger group of suspects, who include retired military officers, politicians, academics and journalists, went on trial in October, accused of being part of a shadowy group known as Ergenekon.
The 2,455-page indictment holds the group responsible for at least two violent attacks - the bombing of a secularist newspaper in 2006 and an attack on a court in the same year, in which a judge was killed.
Attacks on those key parts of the secular establishment were supposed to provoke Turkey's military into launching a coup in defence of secular interests, it is alleged.
The suspects deny the charges, saying they are politically motivated.