A Turkish court on Saturday remanded seven people, including a retired army officer and a top businessman, in custody in connection with an alleged plot to overthrow the government, the Anatolia news agency reported.

It was not immediately clear what charges had been brought against the suspects, who included Sinan Aygun, the head of the Ankara Chamber of Trade who is a known critic of the government, and Atilla Ugur, a retired colonel, the report said.

They were among 21 suspects rounded up earlier this week in dawn raids in five cities as part of a controversial probe into a shadowy network called Ergenekon, that allegedly aimed to discredit and oust the Islamist-rooted government.

The detentions came at a time when the ruling Justice and Development Party was defending itself in court against charges that it is seeking to undermine the country's secular order and should be banned.

Eleven detainees have so far been released, but at least nine of them -- including Mustafa Balbay, the Ankara representative of the secular, anti-government daily Cumhuriyet, and Ilker Guven, a retired vice admiral -- have been barred from leaving the country while the case continues, the agency said.

Two other detainees, retired four-star generals Hursit Tolon and Sener Eruygur, have yet to be formally charged or released by a court.

The Ergenekon investigation was launched in June last year after the discovery of explosives in an Istanbul house, and courts have so far remanded more than 50 suspects in custody.

But the investigation has come under strong criticism because prosecutors are yet to issue an indictment and detail the charges against the suspects.

Critics say the ruling party is deliberately expanding and prolonging the affair to intimidate and silence opponents.