By Tuvan Gumrukcu and Humeyra Pamuk
ANKARA/ISTANBUL (Reuters) - Turkish prosecutors are seeking up to 43 years in jail for journalists from a leading opposition newspaper on charges of supporting a terrorist organisation and targeting President Tayyip Erdogan through "asymmetric war methods".
An indictment seen by Reuters on Wednesday said Cumhuriyet had effectively been "taken over" by the network of U.S.-based cleric Fethullah Gulen, blamed for a failed coup last July, and used to "veil the actions of terrorist groups".
Turkey has purged more than 113,000 people from the police, judiciary, military and elsewhere since the coup attempt, and has closed more than 130 media outlets, raising concerns among Western allies about deteriorating rights and freedoms.
The authorities say the measures are justified by the gravity of the coup attempt, in which rogue soldiers tried to overthrow the government and Erdogan, killing more than 240 people, most of them civilians.
"(Cumhuriyet) started an intense perception operation targeting the government and president of the republic ... through asymmetric war methods," said the 324-page document, parts of which were published by Turkish media on Tuesday.
Cumhuriyet, long a pillar of the secularist establishment, is accused of straying from its principles in the years leading up to the coup attempt and of writing stories that serve "separatist manipulation".
The indictment named 19 journalists, of whom 12 have already been detained, including well-known columnist Kadri Gursel, and Ahmet Sik, who once wrote a book critical of Gulen's movement.
Three of the 19 could face up to 43 years in prison for "aiding an armed terrorist group without being members of it."
The newspaper called the charges "imaginary accusations and slander" and said some of the testimonies in the indictment were from individuals previously seen as close to Gulen.
"Set them free immediately," said its Wednesday front page.
SOCIAL MEDIA POSTS
Prosecutors are seeking 15 years in prison for former editor Can Dundar, jailed in 2015 on charges of publishing state secrets involving Turkish support for Syrian rebels, but later released. Dundar lives in Germany.
Current editor Murat Sabuncu and other senior staff were arrested late last year over alleged support for the failed coup, sparking protests in Istanbul.
Social media posts including Tweets comprised the bulk of evidence in the indictment, along with allegations that staff had been in contact with users of Bylock, an encrypted messaging app the government says was used by Gulen's followers.
Some suspects were accused of "serving the interests" of the PKK militant group, which has waged an insurgency in the mainly Kurdish southeast for three decades, and of the far-leftist DHKP/C, which was behind a series of armed attacks in recent years.
"There are lots of organisations in Turkey. The Gulenist organisation, the PKK, DHKP-C. We are being blamed for helping them all... and it seems I am the prime suspect," Dundar said in a video selfie on his website.
He said the fact Cumhuriyet staff had learned about the indictment in pro-government media was "another legal scandal."
"I stand with all of them and I will continue to be their voice until the end," he said on the website, which he set up from Germany to keep covering Turkish affairs.
(Editing by Nick Tattersall and Jon Boyle)