Those held include the former chief of Turkey's paramilitary forces
Four people detained over a suspected plot against the Turkish government have been remanded in custody.
The four were among 21 suspects rounded up by police in dawn raids across five Turkish cities on Tuesday.
They were suspected of being members of a shadowy ultra-nationalist group known as Ergenekon.
Among the four were the chairman of Ankara's Chamber of Commerce Sinan Aygun and retired Col Atilla Ugur, the state-run Anatolia news agency said.
The other two were not named. It was not clear what charges, if any, have been brought against them.
The highest-ranking officials held in the raids were retired generals Sener Eruygur and Hursit Tolon, both vocal critics of the government. But they have yet to be brought before a court.
Secularists have staged huge anti-AKP rallies
Five others, including a senior journalist, were released on Friday but barred from leaving the country while the case continued, Anatolia said.
The detentions came as the governing AK Party (AKP) was defending itself in court against accusations that it is trying to impose Sharia law and should be banned.
A police investigation against Ergenekon was launched in June 2007 after explosives were found in an Istanbul house.
Courts have so far remanded 54 suspects in custody, including the four on Saturday.
Turkish media said that a secret plan was seized during Tuesday's raids, which included the launching of illegal protests on 7 July across 40 provinces, assassinations and clashes with security forces.
Government critics say the AKP is trying to intimidate and silence its opponents.