ANKARA, Turkey -- Two retired generals were jailed Sunday 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.
Retired 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, were being held at an Istanbul jail.
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.
Labor Minister Faruk Celik urged reporters to wait for their indictments. "We have to trust the republic's prosecutors," he said Sunday. "I believe that as soon as the indictment is released, we will all learn what it is about."
Critics have denounced the arrests as an attempt to silence government opponents. In Ankara, hundreds held a peaceful demonstration to denounce the arrests.
"The day will come when the AKP will be forced to account!" the protesters shouted, referring to the ruling by its Turkish acronym.
Similar protests were staged in other Turkish cities.
Prime Minister Recep Tayyip Erdogan's Islamic-rooted party has been locked in a power struggle with secular groups supported by the military and other state institutions, including the judiciary.
Secularists see themselves as the defenders of the modern secular ideology espoused by Turkish national founder Mustafa Kemal Ataturk, and oppose groups they say want to impose Islam on society.
Earlier in the week, the Constitutional Court heard allegations against the ruling party of anti-secular activity. The prosecutor wants the party disbanded, and Erdogan and 70 other party members banned from joining a political party for five years.
The prosecutor cited the government's attempt to permit Islamic-style head scarves at universities -- which the Constitutional Court last month ruled unconstitutional.
Erdogan's party, formed in 2001 by politicians who once belonged to Turkey's Islamic movement, denies it has an Islamic agenda, noting that it has backed reforms to help Turkey start EU membership negotiations.
The investigation into "Ergenekon" was launched last year after hand grenades issued to security forces were found at the Istanbul home of a retired military officer. The chairman of Ankara's chamber of commerce also was arrested Saturday, and a prominent journalist with a pro-secular newspaper was released pending trial.
"Those who believe in Ataturk, in the secular republic, are under attack," said Deniz Baykal, leader of the opposition Republican People's Party.