ANTAKYA, Turkey — A law enforcement raid on a prominent media company and takeover of the nation’s largest-circulation newspaper have raised new fears of a press under assault by the administration of Turkish President Recep Tayyip Erdogan.

Police late Friday forced their way into the offices of Zaman newspaper and its English-language sister publication, Today’s Zaman, after an Istanbul court ordered the seizure of Feza Media Group, which owns the two dailies.

Police in riot gear peppered protesters and staff alike with volleys of tear gas and water cannons, a scene broadcast live on satellite television.

Both papers are linked to the Cemaat movement, which is led by the U.S.-based Muslim cleric, Fethullah Gulen, a one-time Erdogan ally whose followers have become fierce rivals of the Turkish president. The Turkish government has labeled Cemaat a terrorist organization.

Addressing a crowd of supporters Friday waving placards reading “Do not touch my newspaper,” Today’s Zaman editor-in-chief Sevgi Akarcesme described the takeover as “a shameful day for media freedom in Turkey.”

“Our media institutions are being seized,” she said. “As of today, the constitution has been suspended.”

Zaman has a daily circulation of more than 600,000, the largest in Turkey.

Amnesty International described Friday’s actions as “deeply troubling.”

“By lashing out and seeking to rein in critical voices, President Erdogan’s government is steam rolling over human rights,” Amnesty International’s Turkey expert, Andrew Gardner, said in a statement.

The shutdown also drew an unusually forceful rebuke from the U.S. State Department, which is generally hesitant to criticize Turkey, a NATO ally.

At a regular news briefing Friday, a State Department spokesman, John Kirby, said the raid was “the latest in a series of troubling judicial and law enforcement actions” and was not “in keeping” with Turkey’s constitution.

“Critical opinions should be encouraged, not silenced,” Kirby said.

The case is the latest instance in which Turkish authorities have targeted the opposition media. In October, days before the country’s general election, Turkish authorities ordered the seizure of Koza Ipek Group, which ran several prominent television stations critical of the government.

The government-led crackdown on opposition media is having a chilling effect on Turkey’s press, media advocates say.

Pro-government protesters led by prominent ruling party figures have intermittently surrounded opposition newspaper offices, pelting them with stones and smashing windows. Scores of journalists have lost their jobs under government pressure, according to press freedom groups.

Turkish newspapers often tend to be partisan, analysts note, blurring the distinction between media and politics — in effect making opposition newspapers Erdogan’s political rivals.

“Media here is so politicized that we often don’t know what is ‘real’ news and what is not,” said Huseyin Bagci, head of the international relations department at Ankara’s Middle East Technical University. “But the government is absolutely determined to suppress any opposition.”

Critics say the media crackdown demonstrates Erdogan’s authoritarian streak and lack of tolerance of dissent.

The Turkish government has come under strong internal criticism for a number of controversial policies. Those include ongoing military operations against Kurdish groups in the southeast and the extensive effort to back rebel factions, including militant Islamists, fighting to overthrow the secular government of President Bashar Assad in neighboring Syria.

Prosecutors have opened at least 1,845 cases of “insulting the president” since Erdogan rose to the presidency in August 2014 with 52% of the vote.

Among those who have been charged are celebrities, a former Miss Turkey beauty queen and children who tore down a poster depicting Erdogan. A public health worker, Bilgin Ciftci, was even accused of “insulting” Erdogan for sharing pictures on social media likening the president to the creature Gollum from “The Lord of the Rings.”

“These cases often appear to be intimidation,” said Ergun Ozbudun, a Turkish constitutional law expert.

Highlighting the often hostile media environment was the case of IMC TV, an independent channel that had its signal cut last month in the middle of a broadcast interview with a pair of journalists who had just been released from jail.

Prosecutors contended that the channel was spreading terrorist propaganda.

The channel reports extensively from Turkey’s predominantly Kurdish southeast, where Kurdish militants and Turkish authorities have been engaged in bitter urban conflict with government forces since July.

The channel’s signal was cut as its anchor was interviewing Can Dundar and Erdem Gul, respectively the editor-in-chief and Ankara Bureau Chief of Cumhuriyet newspaper — a left-leaning newspaper often critical of the government.

Prosecutors had sought life sentences for the two journalists, charging that the pair had supported a terror organization, threatened state security and engaged in espionage. The journalists said they were just doing their jobs.

In May last year, Cumhuriyet published a sensational report that allegedly showed trucks, halted by police in southeastern Hatay province, belonging to Turkey’s National Intelligence Agency, stacked full of ammunition destined for insurgents in neighboring Syria.

The two journalists were arrested and sent to prison to await trial. After 92 days, Turkey’s Constitutional Court last week ordered their release on grounds that their personal rights had been violated.

The Turkish president fumed at the court decision, publicly refusing to “respect or obey” it.