A Turkish court has put Zaman newspaper - a vocal critic of President Recep Tayyip Erdogan - under state control.
Administrators have been appointed to run the newspaper. There is no explanation for the court's decision.
Zaman is closely linked to the Hizmet movement of influential US-based cleric Fethullah Gulen, a former Erdogan ally.
Turkey describes Hizmet as a "terrorist organisation" aiming to overthrow the government. Many of its supporters have been arrested.
Mr Erdogan's government has come under increasing international criticism over its treatment of journalists.
Freedom of the press in Turkey
- Turkey ranks 149th amongst the 180 countries in the Reporters Without Borders' World Press Freedom Index 2015
- Media organisations in Turkey say that more than 30 journalists are currently behind bars
- Most are of Kurdish origin
- The government argues journalism in Turkey is among the most free in the world
In a statement, Zaman said the country was going through its "darkest and gloomiest days in terms of freedom of the press".
It expressed "deep concern" at the latest court order - the culmination of pressure for more than two years on Turkey's "highest circulating newspaper, Zaman, and its sister publication Today's Zaman". It said the pressure had been through "accreditation bans, tax inspections, meddling with its advertisers and threats to its readers".
Editor-in-chief Sevgi Akarcesme told Reuters news agency this was "the practical end of media freedom in Turkey".
"The media has always been under pressure, but it has never been so blatant," she said.
Steamrolling over rights
Dozens of supporters gathered outside the paper's Istanbul headquarters after the announcement of the court decision.
One held a placard saying, "We will fight for a free press."
Amnesty International's Andrew Gardner said: "By lashing out and seeking to rein in critical voices, President Erdogan's government is steamrolling over human rights.
"A free and independent media, together with the rule of law and independent judiciary, are the cornerstones of internationally guaranteed freedoms which are the right of everyone in Turkey," he said.
The move against Zaman comes days after Turkey's Constitutional Court ordered the release from detention of two Turkish journalists charged with revealing state secrets.
Can Dundar and Erdem Gul, from the newspaper Cumhuriyet, were detained in November over a report alleging that the Turkish government tried to ship arms to Islamists in Syria.
The pair still face possible life sentences at their trial on 25 March.
Two newspapers and two television channels were put under state administration last year over their alleged links with the Hizmet movement.
The Turkish government has accused Mr Gulen, Hizmet's spiritual leader, of trying to run a parallel state.
On Friday, state-run Anadolu news agency said police had detained four senior officials of a company linked to Mr Gulen in the central city of Kayseri.
Turkey has asked the US to extradite Mr Gulen. The exiled cleric has allies in the Turkish police and judiciary, media and financial interests as well as a network of schools.
- Inspired by the teachings of Islamic preacher Fethullah Gulen, who lives in the US
- 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 across more than 150 countries
- First expanded into Central Asia after the USSR's demise in 1991