Early Monday morning, Turkish police detained Murat Sabuncu, editor-in-chief of the newspaper Cumhuriyet, along with a dozen other reporters in a raid, according to official news agency Anadolu.
The Turkish government has accused the journalists of publishing stories to "legitimize the coup d'etat" just before the July 15 coup attempt. The journalists are accused of crimes on behalf of enemies of the state.
Supporters of the newspaper, including opposition politicians, protested the move outside the publication's Istanbul offices Monday.
The arrests followed a weekend during which more than 10,000 public servants were fired and over a dozen media companies were shut down.
Clampdown on critical journalists
Cumhuriyet, a nearly century-old secular opposition newspaper, has remained critical of Turkish President Recep Tayyip Erdogan, along with his ruling AKP party.
Last year the paper's former editor-in-chief, Can Dundar, was taken into custody over a story published about the Turkish intelligence service allegedly sending weapons to Syrian opposition.
According to Anadolu, Turkish police also searched the houses of two other journalists.
Istanbul's chief prosecutor has said the journalists detained Monday weren't just accused of "being members of FETO and PKK terrorist organizations but committing crimes in the name of those terror organizations."
FETO is the name of the movement affiliated with US-based cleric Fethullah Gulen.
Turkey blames FETO and the PKK, the Kurdistan Workers' Party, of being terrorist organizations involved in the failed July coup.
Amnesty International's Europe Director John Dalhuisen called the arrests a "blatant misuse" of the emergency powers introduced to crack down on alleged coup plotters and called for the immediate release of the detained journalists.
"Today's detention of journalists and staff from Turkey's only remaining mainstream opposition newspaper is part of an ongoing systematic attempt to silence all critical voices," he said in a statement.
"Together with the shutting down of media houses over the weekend, this is the latest wave in a post-coup purge which has turned Turkey's once vibrant media landscape into a wasteland."
Earlier this month, another raid on Istanbul-based IMC TV, an opposition-affiliated, pro-Kurdish channel, came
as the station was reporting on the government's closure of another television channel. Turkish authorities cut IMC's transmission in the middle of the broadcast.
10,000 officials fired
Under a legislative decree published Saturday, Turkish authorities fired more than 10,000 public servants for alleged ties to the movement affiliated with Gulen,
and shut down 15 Kurdish media companies for alleged ties to militant Kurdish groups, Anadolu reported.
The new decree "made it easier to sack public officials believed to be members of terrorist organizations or groups involved in activities against the country's national security," Anadolu reported.
The 10,131 dismissed government employees were alleged to have ties to Gulen.
The decree also effectively grants Erdogan the power to appoint all the heads of Turkey's universities by abolishing a system in which academics picked the top candidates for rectors of the schools. Academics had selected a slate of rector candidates at the institutions for more than two decades.
The 15 Kurdish media companies that were shut down are accused of ties to the PKK, which has been battling the Turkish state off and on for some 30 years.
Turkey, the United States and the European Union consider the PKK to be a terrorist organization.
The media shutdown is the latest in an escalation of moves against prominent Kurds.
On Tuesday, authorities detained the two elected mayors
of the predominantly Kurdish southeastern city of Diyarbakir, also over alleged PKK "terror links."
Separately, a court in the mainly Kurdish southeastern city of Diyarbakir arrested the two elected mayors of the city on alleged terror charges. According to the state's official news agency, co-mayors Gultan Kisanak and Firat Anli were being investigated for ties to Kurdish groups that Turkey considers terrorists.
In September, the government appointed trustees to more than two dozen municipalities in mainly Kurdish cities, replacing their elected mayors.
Rising tensions sparks US travel warning
The move follows a travel warning from the State Department.
"The Department of State made this decision based on security information indicating extremist groups are continuing aggressive efforts to attack US citizens in areas of Istanbul where they reside or frequent," the warning said.
A travel warning for southeast Turkey, especially urban centers near the Turkish-Syrian border, has been in effect since Monday.