Turkish authorities targeted Friday opposition daily Sozcu, seeking the arrest of the owner and detaining two employees as the crackdown on opposition media widened.
The owner, Burak Akbay, and three others, including the executive in charge of the website, Mediha Olgun, are accused of links to the movement led by Islamic preacher Fethullah Gulen blamed for last year's failed coup, Anadolu news agency reported.
The fiercely anti-government and ultra-secularist daily whose name means "spokesman" is one of the country's bestselling papers. Its slogan is: "If #Sozcu is silent, Turkey will be silent."
Istanbul prosecutors issued four arrest warrants including correspondent Gokmen Ulu and Yonca Kaleli, a finance executive, CNN Turk broadcaster said.
Ulu, who reports from the western city of Izmir, was later detained by police and officers searched his home, the state agency said, after Olgun had been taken into custody earlier in the day.
The daily confirmed Olgun and Ulu's detention on its website Friday evening while CNN Turk said Akbay was in London.
"We have fought against terrorist organisations, FETO. As journalists, we have written the truth when they have committed large wrongs against this country," Ulu told reporters earlier in the day before he was taken into custody.
Istanbul prosecutor Irfan Fidan confirmed the operation into "Sozcu's executives", saying "there are warrants, there are detentions" without giving details.
Owner Akbay later said he was "being targeted because I produce right and honest journalism" in a statement on the daily's website.
Sozcu's lawyer Ismail Yilmaz denied arrest warrants had been issued, saying warrants had been issued to seize and search their belongings.
And Yilmaz suggested earlier Olgun's detention could be in connection with another investigation, the private Dogan news agency reported.
The four are accused of "committing crimes on behalf of an armed terror organisation", referring to the Gulen movement, CNN Turk reported.
Turkey refers to the movement as the "Fethullah Terrorist Organisation" (FETO), but Gulen vehemently denies ordering the coup and the movement denies any terror charges.
CNN Turk said the suspects were wanted in connection with an online article published on the same day as the attempted coup on July 15.
The accusations levelled at them include attempted "assassination and real attack of the president" and involvement in an "armed rebellion against the government", Anadolu said.
The article in question revealed details of where President Recep Tayyip Erdogan was on holiday in the upmarket Aegean resort of Marmaris, CNN Turk said, and had images of his hotel.
Sozcu is the second daily to be targeted after another leading opposition newspaper Cumhuriyet saw 20 staff members charged under the state of emergency imposed following the attempted putsch.
The daily is on occasion rabidly anti Erdogan and its angry front pages are regarded with some suspicion by some liberal Turks critical of the president.
Its sometimes lurid approach contrasts with the more moderate tone of Cumhuriyet, one of the country's oldest dailies.
Main opposition Republican People's Party (CHP) leader Kemal Kilicdaroglu said the "detention, arrest and pressure on journalists was something no democracy could accept" as he visited the paper's offices in Istanbul.
The warrants for Sozcu come as people commemorate modern Turkey's founder Mustafa Kemal Ataturk on "Ataturk, Youth and Sports Day".
Sozcu writer Ugur Dundar reacted to the news on Twitter, saying: "On a national holiday, there are detentions from Sozcu. I will go to my newspaper Sozcu. If Sozcu is FETO, everyone in Turkey is FETO!"
Sozcu's front page on Friday had a large image of Ataturk with the headline: "The biggest leader in 100 years" accompanied with the usual image of his eyes next to the paper's name.
The daily issued a statement of defiance on its website: "Let no one have any doubt, Sozcu will not be silent. It will continue to be the voice of this country's conscience."
Kati Piri, the European Parliament's rapporteur for Turkey, criticised the operation on Twitter: "In Turkey critical journalism is equaled with terrorism. Attack on Sozcu newspaper another sad example."
According to the P24 press freedom website, there are 165 journalists behind bars in Turkey, most detained as part of the emergency imposed after the coup bid.
More than 100 media outlets have been closed down since mid-July.
Turkey ranks 155th out of 180 countries in Reporters Without Border's 2017 World Press Freedom Index.