Turkish police have made at least 23 arrests during raids on a newspaper and TV station with close ties to US-based Islamic cleric Fethullah Gulen.
Those detained are accused of forming an illegal organisation and trying to seize control of the state.
Mr Gulen, the spiritual leader of the Hizmet movement, is a rival of Turkish President Recep Tayyip Erdogan.
The raids come days after Mr Erdogan pledged a fresh campaign against Mr Gulen's supporters.
Among those arrested are journalists, producers, scriptwriters and a police chief in eastern Turkey.
Police attempted to raid the offices of the Zaman newspaper, one of Turkey's biggest, early on Sunday morning, but a crowd of protesters forced police to turn back before they could make arrests.
Staff at the paper also reported on the incident as it happened.
The paper's editor-in-chief, Ekrem Dumanli, tweeted a picture of himself at his desk, saying: "Officers [forced] back because of democratic reaction of my friends. I am at my place and wait."
But they returned and arrested him in a second raid in the afternoon.
Staff and supporters of the paper held placards and chanted "free press cannot be silenced" as police raided the building.
Mr Dumanli smiled and studied police documents before being led through the newspaper's headquarters to applause from staff crowded onto balconies.
"Let those who have committed a crime be scared," Mr Dumanli said as he was led away, according to Reuters.
"We are not scared."
Analysis by Mark Lowen, BBC News, Istanbul
The timing of these arrests isn't coincidental. It's almost a year to the day since the biggest corruption scandal in Turkey's modern history exploded. Recep Tayyip Erdogan, then prime minister, now president, was targeted, along with his inner circle. Four ministers were forced to resign. It was widely believed the government wouldn't survive.
Extraordinarily, Mr Erdogan managed to turn it around, declaring war on what he called a "parallel state": followers of his one-time ally Fetullah Gulen who he said were plotting a coup. He fired thousands of police officers and prosecutors, launching an endless tirade in the media that he's ensured is widely pro-government, and sidelined dissidents. This is stage two: arresting the critics.
Turkey already ranks 154th of 180 in the press freedom index compiled by Reporters without Borders. Human rights organisations raise concerns that freedom of expression is under attack in a country seeking EU membership.
But the Turkish government says it's a conspiracy against a country that won't toe the West's line. It talks of the "enemy within" which must be eradicated. Today's move will fuel international concerns of an eroding democracy here.
The chairman of Samanyolu TV, which also has links to Mr Gulen, was detained in a separate raid in Istanbul.
Hidayet Karaca told reporters the operation was "a disgrace for Turkey" before his arrest.
"Sadly in 21st Century Turkey this is the treatment they dish out to a media group with tens of television and radio stations, internet media and magazines," the English edition of Zaman quoted him as saying.
Kemal Kilicdaroglu, the leader of Turkey's main opposition party, called the raids "a coup".
Staff at Zaman had been expecting the raid after details of the swoop were leaked by a Twitter user known as Fuat Avni, who has previously leaked advance details of police operations.
The police operation comes a year after corruption allegations against allies of Mr Erdogan emerged. He said it was a plot orchestrated by Mr Gulen supporters to topple him.
Mr Gulen denied this. He has lived in self-imposed exile in the US since 1999.
On Friday Mr Edogan vowed to pursue Gulen supporters "in their lairs".
- Hizmet ("Service") is the Turkish name for what is commonly known as the Gulen movement
- The movement is inspired by the teachings of Islamic preacher Fethullah Gulen, who lives in exile in the US
- Mr Gulen is a mainstream Sunni Hanafi Muslim scholar, influenced by Anatolian Sufism
- There is no formal structure but Hizmet followers are numbered in the millions, spread across more than 150 countries
- First expanded into Central Asia after the Soviet Union collapsed in 1991.