Istanbul, Turkey (CNN) -- The four-year investigation into an alleged plot to overthrow Turkey's government just keeps getting bigger. But as police arrest more and more journalists accused of aiding the coup plot, press freedoms groups are expressing alarm.
With more than 50 reporters currently behind bars in Turkey, activists argue freedom of expression is under fire in a country that is often promoted as a model Muslim democracy for the turbulent Middle East.
Meanwhile, many writers claim that a new taboo has emerged in this Byzantine web of politics, power and press... an enigmatic Muslim cleric who leads a vast network of international schools and businesses from his home in exile, a farm in the U.S. state of Pennsylvania.
Last March, police swept through the Istanbul homes of two high-profile investigative journalists, seizing documents and detaining the reporters: Posta newspaper columnist Nedim Sener and online news editor Ahmet Sik.
These arrests came after police detained the editors of Oda TV, a hard-line secularist internet news portal that often criticized the government of prime minister Recep Tayyip Erdogan.
The journalists have yet to be formally charged. They join hundreds of other jailed suspects awaiting trial in the sprawling investigation into "Ergenekon," an alleged gang led by ultra-secularist Turkish military officers aimed at toppling Erdogan's Islam-inspired government.
Supporters of the Ergenekon investigation argue it is "demilitarizing" Turkish society.
But the arrests have spread fear among many Turkish reporters.
On a chilly and rain-soaked day last month, several hundred journalists marched through the streets of Istanbul, waving signs saying "Hands Off My Opinion."
"We are here to protest the growing repression over Turkish media by the Turkish government for the last couple of years," said Can Dundar, a well-known columnist and anchorman for Turkey's NTV.
"We want to be free to write. We want to be free to talk and we want to be free to publish our books without any repression or fear," he added.
"At present, 57 journalists are in prison in Turkey and the number of ongoing trials that can result in imprisonment of journalists is estimated to be from 700 to 1,000," said Dunja Mijatovic, the representative on freedom of the media for the Organization for Security and Cooperation in Europe in a recent report.
Meanwhile, in a report issued this week on World Press Freedom Day, the Washington-based watchdog organization Freedom House rated Turkey "partly free." Turkey, which is currently negotiating to join the European Union, was ranked 112 out of 196 countries, next to Bangladesh, Congo-Brazzavile, and Uganda.
In an interview with CNN last November, Sener ominously predicted that he might be targeted for his criticism of the Turkish government.
"Today there is direct pressure from the political authority. They can easily corner the reporter they don't like for news they don't like and act in ways that can lead to getting fired," said Sener, who received a World Press Freedom Hero award from the International Press Institute for his book investigating the 2007 assassination of Turkish-Armenian newspaper editor Hrant Dink.
Turkish government officials deny claims the media atmosphere is growing increasingly intolerant.
"The issue here is not the big bad government trying to silence the press," wrote Egemen Bagis, Turkey's European Union integration minister, in the pro-government newspaper Today's Zaman.
"Despite the expression of concern from the highest echelons of the state on the arrest of the journalists, the prosecutors have clearly stated that they have evidence that links the journalists to the Ergenekon terrorist group," Bagis added.
Some observers, including the two recently detained reporters, have observed a pattern of arrests targeting critics of an enigmatic figure on the Turkish political scene... the influential Muslim cleric and powerful supporter of the Turkish government Fethullah Gulen.
From his home in exile on a farm in Pennsylvania, Gulen is the inspirational leader of an enormous network of schools and universities operating in more than 120 countries around the world. He speaks to his followers through a small empire of pro-Gulen newspapers, publication houses and TV stations in Turkey as well as over the internet. During his victory speech after winning a referendum on constitutional reform last year, Erdogan took care to thank his "friends across the ocean"...code-words for the Gulen movement.
"The government... and the Fethullah Gulen group are the taboos in Turkey. It is very dangerous to write about these in Turkey and I write about them," said investigative journalist Sener said in his November 2010 CNN interview.
Meanwhile, as he was being led from his house to a waiting police car, the arrested journalist Ahmet Sik yelled out to the crowd of people gathered on the street, "If you touch him, you will burn."
When he was arrested, Sik was in the midst of writing a critical book about the Gulen movement titled "The Imam's Army." Police seized his book as evidence.
Another author of a recent book slamming the Gulen movement is also behind bars. In "Devotees on the Golden Horn: Yesterday's State, Today's Religious Movement," former police commander Hanefi Avci claimed supporters of Gulen had infiltrated the Turkish police force. He also accused the "Gulenists" of illegally tapping telephones. A month after the book was published, police arrested Avci. He now stands accused of being a member of a leftist terrorist organization, a charge Avci denies.
Gulen's supporters deny claims that it is dangerous to criticize the movement in print.
"This is a smokescreen campaign and this is also a psychological war," said Professor Ihsan Yilmaz, a political scientist at the Gulen-operated Fatih University in Istanbul.
Faruk Mercan, one of Gulen's biographers, pointed out that other authors have written dozens of other critical books about the reclusive evangelist without facing prosecution. And he argued that the media had often worked in close collaboration with the Turkish military, when it overthrew four elected governments in coups over the last 60 years.
"When you look at Turkish history you can see there are very famous Turkish journalists involved in military coups," Mercan said. "Now is the time for post-modern coups in which un-armed forces like the media or civil society organizations are basically fulfilling a similar task."
After dominating Turkish politics for decades, the military and its allies in secularist political parties have has been in retreat. Since his Justice and Development Party swept to power in 2002, Turkey's fiery prime minister has repeatedly defeated his secularist opponents both at the ballot boxes and in the courts. Initially, Erdogan made joining the European Union a top national priority.
"I thought that Turkey was becoming a more liberal place," said Andrew Finkel, a Canadian journalist who has lived and worked for years in Turkey. "I thought that if you dismantle the military apparatus... that the country would be freer."
Finkel, a free-lance contributor to CNN, had to defend himself in Turkish courts in 1999 and faced a possible six-year jail sentence, after he was accused of "insulting the military" in an article he wrote. More than a decade later, Finkel said he ran afoul of the new powers-that-be that govern Turkey.
After spending the last four years writing a column for the Gulen-owned Today's Zaman, Finkel was fired last month.
He claimed he lost his job because of his last, unpublished column written in defense of the jailed journalists.
"I was criticizing my own newspaper for not being vocal enough in the defense of freedom of expression. I felt we should be doing more about people seizing books, about being more tolerant even if those books were against us," Finkel said.
The editor of Today's Zaman denied these accusations.
"No newspaper is obligated to work with all of its writers until the end of time," wrote Bulent Kenes in an editorial last month. "What has changed is that some of our writers have come under the influence of the strong and dark propaganda that is at play and have started to stagger. Unfortunately, I feel the same way about Finkel."
The stark polarization of Turkish politics and media is likely to get worse in the final weeks before parliamentary elections on June 12. Polls predict Erdogan will win a third term in office. This week, on World Press Freedom Day, Turkish journalists made another appeal to Erdogan, to better protect a fundamental democratic right.