ANKARA, Turkey — Today prosecutors charged 86 nationalists, including former army officers and a best-selling writer, of plotting to overthrow Turkey’s Islamic-oriented government, escalating a power struggle between the ruling party’s supporters and secular forces.

The chief prosecutor at Istanbul, Aykut Cengiz Engin, said the suspects were charged either with forming or belonging to a terrorist organization, or of provoking an armed uprising with the aim of bringing down Prime Minister Recep Tayyip Erdogan’s government.

The suspects are believed to be part of a nationalist network called Ergenekon, which takes its name from a legendary valley in Central Asia believed to be the ancestral homeland of Turks.

The opposition says the case smacks of a political revenge against secularist groups — including the military — at a time when the country’s top court is deliberating whether to disband the ruling party for alleged anti-secular activity.

Mr. Erdogan’s supporters on the other hand, say the lawsuit will help strengthen democracy in a country that has experienced several military interventions in the past half century. The military staged three coups since the 1960s and in 1997 pressured an Islamic party out of power.

The indictment accuses the suspects of “attempting to prevent the functioning of the Turkish government or of eradicating it, by using oppression and force,” the prosecutor said.

The suspects allegedly devised plans to create a climate of civil unrest to provoke a military coup.

The prosecutor did not name those charged but they are believed to include at least one retired general and an opposition politician, who were arrested over the past year.

Hardline secular Turks believe Mr. Erdogan’s government is trying to erode Turkey’s secular laws and is making too many concessions on national interests to join the European Union.

A court will decide within two weeks whether to open the case.

Turkey’s military has staged three coups since the 1960s and in 1997 pressured an Islamic party out of power. The coup in 1980 followed a period of civil strife.

The military last year threatened to intervene when Mr. Erdogan nominated his close political ally, Abdullah Gul, for the presidency.

A military court prosecutor has demanded to see documents relating to the case, suggesting that the military was leading its own investigation into the alleged plotters, private NTV television and others reported today.

Without the backing of the military command, retired generals would have a very hard time staging a coup, analysts say.

But the alleged plots show the scope of the unease and animosity felt toward the government. The indictment comes as the government is trying to strengthen democracy in the hope of getting Turkey admitted to the EU.

“This is a campaign to defame people who speak against the government,” a member of the secular opposition party, the Republican Peoples’ Party, Onur Oymen, said.

A senior member of Mr. Erdogan’s Justice and Democracy Party, Bekir Bozdag, denied the accusation saying: “the judiciary is independent, it is not possible for the government to be involved in the process.”

The suspects were detained after police uncovered a cache of hand grenades at the house of a retired noncommissioned officer in Istanbul last summer. The investigation intensified after Mr. Erdogan vowed to crack down on shadowy “deep state” gangs — a network of renegade agents within the state who may be taking the law into their own hands.

Forty-eight of the suspects have been jailed. They include an ultranationalist lawyer, Dogu Perincek, a small leftist and nationalist party leader, and Ergun Poyraz, who wrote a series of best-sellers critical of Mr. Erdogan.

The prosecutor said an additional indictment is being prepared against a dozen other people, including two senior retired generals, who were arrested early this month for their alleged ties to the group. The two would have been serving officers when the coup plots were being devised, newspapers have reported.

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Associated Press Writer Selcan Hacaoglu contributed to this report.