Turkey's former army chief Ilker Basbug was arrested Friday for an alleged bid to topple the militants-rooted government in the latest confrontation likely to inflame tensions with the powerful military.
"The 26th chief of staff of the Turkish republic has unfortunately been placed in preventive detention for setting up and leading a terrorist group and of attempting to overthrow the government," Ilkay Sezer, a lawyer for Basbug, was quoted as saying by the Anatolia news agency.
He is the first such high-ranking military commander to be held as a suspect since another former chief of staff in the 1960s, according to the Turkish press.
However, dozens of active and retired military officers, academics, journalists and lawyers have been detained in recent years in probes into alleged plots against the government of Prime Minister Recep Tayyip Erdogan.
The United States swiftly urged Turkey to ensure Basbug is treated fairly following his arrest.
State Department spokeswoman Victoria Nuland said Washington was monitoring developments in what she called a "high-profile case" that is part of a wider probe into the so-called Ergenekon network.
"We have urged the Turkish government to ensure that the investigations, any prosecutions in... these cases proceed in a transparent manner, that all the defendants be assured due process in accordance with international standards," she said.
Basbug, who retired in 2010, is the most senior officer to be implicated in a massive investigation into the so-called Ergenekon network, accused of plotting to topple Erdogan's Islamic-rooted Justice and Development Party (AKP).
His arrest came hours after he testified as a suspect at an Istanbul court on Thursday as part of a probe into an alleged Internet campaign to discredit the government.
"The commander of such an army facing charges of forming and leading an armed organisation is really tragicomic," the 68-year-old general told prosecutors, Anatolia reported.
"I always followed the law and the constitution throughout my tenure."
Tensions between Turkey's fiercely secularist military and Erdogan's government have been building for years, and now about one tenth of the army's generals are in custody over the alleged coup plots.
Basbug, who served as army chief from 2008 to 2010, was sent to Istanbul's Silivri prison where other suspects of the alleged Ergenekon network are being detained. His lawyer said he would challenge the court's ruling.
"Nobody can be declared guilty without a court decision," said Turkish President Abdullah Gul, a close Erdogan ally whose 2007 election was met with fierce opposition from the military.
"Everybody is equal before the law."
The military, which considers itself as the guardian of secularism in modern-day Turkey and currently boasts a force of 515,000 troops, has carried out three coups -- in 1960, 1971 and 1980.
In 1997, the army also forced the removal of a coalition government led by an Islamist prime minister.
"We are witnessing history," Nihat Ali Ozcan, security analyst at the Ankara-based TEPAV think tank, told AFP. "I believe Basbug's arrest will have a catastrophic impact on the military in the medium term.
"And on the political front, it will lead to polarisation between those who defend the legal process in the name of democracy and those who consider it authoritarianism under one-party rule."
The move against Basbug appears to be a fresh warning to the army in Turkey -- the largest of the NATO member states after the United States -- whose political influence has waned since Erdogan's AKP came to power in 2002.
Critics accuse Erdogan's government of launching the Ergenekon probes as a tool to silence its opponents and impose authoritarianism, charges it denies.
But even those close to government circles have voiced doubts about the legitimacy of the investigations, especially after the arrest of two prominent investigative journalists, Ahmet Sik and Nedim Sener.
Among the accusations levelled against Basbug is an alleged attempt by a group of army officers to establish websites to disseminate anti-government propoganda in order to destabilise the country.
"I reject this charge... I, as the chief of the general staff, am the commander of the Turkish armed forces which is one of the most powerful armies in the world," Basbug said in his testimony, according to Anatolia.
Kemal Kilicdaroglu, leader of Turkey's opposition Republican People's Party (CHP), said the courts trying the Ergenekon suspects were not delivering justice.
"They are implementing decisions made by the political authority," he was quoted as saying by Anatolia.