The document is the first to emerge from a year-long investigation into an alleged ultra-nationalist network dubbed "Ergenekon".

The ruling Justice and Development Party (AKP), facing legal action that could lead to it being outlawed, has been accused of using the probe to silence its opponents.

The 2,455-page indictment includes charges of creating an "armed terrorist organisation", using violence to unseat the government and provoking an armed uprising, Istanbul chief prosecutor Aykut Cengiz Engin told a news conference.

The indictment drawn up by three prosecutors also accuses defendants of instigating attacks including the 2006 bombing of a pro-secular newspaper and an armed attack on a top court the same year that killed a senior judge, Engin said.

"The terrorist organisation mentioned in the indictment is not a separatist or ideological organisation in the classic sense," Engin said.

He said 48 of the 86 suspects indicted were in custody, but did not say who they were and which charges each faced.

Engin said he was legally barred from giving further details on the case, as the indictment must be approved by the Istanbul criminal court to which it was sent before the trial can proceed.

The prosecutor says the charge sheet does not include 20 other suspects, including two retired four-star generals, who were detained earlier this month as part of the investigation.

A second indictment will be prepared against these latest suspects once prosecutors complete their investigation, Engin said.

The Istanbul prosecutor's office has been investigating "Ergenekon" since police discovered explosives in an Istanbul house in June 2007.

Media reports said the group was plotting to foment unrest through illegal protests, assassinations and clashes with security forces to provoke a military coup against Prime Minister Recep Tayyip Erdogan's government.

The Turkish military, which has unseated four elected governments in as many decades, is largely distrustful of the AKP for its roots in a now-banned Islamist movement.

The Ergenekon investigation has raised tensions at a time when the AKP is fighting legal action brought by the country's top prosecutor to have the party banned for undermining the secular system.

Critics note that most of those detained in the Ergenekon investigation include opponents of the AKP and accuse the party of using the probe to counter-attack the closure case.

The AKP denies that it wants to install an Islamist regime in Turkey and says it is fully committed to the separation of state and religion.

But hardline secularists -- among them the army, the judiciary and some academics -- say moves such as easing restrictions on the Islamic headscarf and banning alcohol sales in establishments run by AKP municipalities point to a secret Islamist agenda.

The Constitutional Court is expected to rule in the AKP case as early as next month.

Istanbul chief prosecutor Aykut Cengiz Engin