Turkish police have detained the editor and at least 12 senior staff of Turkey’s opposition Cumhuriyet newspaper in a widening crackdown on dissenting voices.

The editor-in-chief, Murat Sabuncu, the cartoonist, Musa Kart, the paper’s lawyer and several columnists were detained, some following raids at their homes, Cumhuriyet reported on its website. Police had warrants for the detentions of 16 staff members, the paper said.

The detentions at the left-leaning and pro-secular Cumhuriyet, one of Turkey’s oldest newspapers, come amid accusations by opposition parties and human rights groups that Turkey’s government is using the state of emergency imposed following a failed military coup in July to clamp down not only on the alleged coup plotters but on all government critics.

A statement from the Istanbul chief prosecutor’s office said those detained were suspected of “committing crimes” on behalf of the movement led by US-based Muslim cleric Fethullah Gülen, accused by the government of masterminding the coup attempt as well as the outlawed Kurdistan Workers’ party, or PKK.

While those detained are not accused of membership of the Gülen movement or the PKK, there are “claims” and “proof” that shortly before the 15 July coup attempt, the suspects published content that attempted to legitimise the coup, the statement said. Gülen, who lives in the US, has denied any involvement in the coup attempt.

Authorities have arrested nearly 37,000 people following the coup and more than 100,000 people have been dismissed or suspended from government jobs in a purge to eradicate Gülen’s network. Over the weekend, the government issued two decrees that dismissed 10,000 additional civil servants and shut down 15 more mostly pro-Kurdish media outlets.

Sibel Günes, the general secretary of the Turkish Journalists’ Association, told the Associated Press that 170 media outlets had been shut down since the attempted coup and 105 journalists arrested. Authorities revoked the press accreditation of more than 700 journalists while thousands of journalists are unemployed, Günes said.

Opposition politicians rushed to Cumhuriyet’s headquarters in Istanbul and its office in the capital, Ankara, in a show of solidarity. Hundreds of demonstrators also gathered, chanting anti-government slogans.

“Instead of moves to strengthen democracy we are faced with a counter-coup,” the main opposition party leader, Kemal Kılıçdaroğlu, said after visiting the newspaper. “We are faced with a situation where the coup has been used as an opportunity to silence society’s intellectuals and mount pressure on media.”

Christophe Deloire, who heads Reporters Without Borders, said on Twitter that “the raids against media in Turkey seem to have no limits”. Those wanted for detention include columnist Kadri Gürsel, who also heads the Turkish national committee of the media advocacy group International Press Institute. He tweeted that his house was being searched.

Ayşe Yıldırım, a Cumhuriyet columnist, said the detentions could be a prelude towards a government takeover of the newspaper.

“We are not going to hand over Cumhuriyet, we are not going to allow them to assign a trustee. We will hold our heads high and continue our publication without fear,” she said outside the paper’s Istanbul headquarters.

As he left the building to surrender to police, Kart told reporters: “How will they explain this to the world? I am being taken into custody for drawing cartoons.” Kart has been prosecuted in the past for insulting the Turkish president, Recep Tayyip Erdoğan.

The Anadolu agency said the authorities had also issued an arrest warrant for the paper’s former editor-in-chief, Can Dündar, who was sentenced to five years in prison in May for reports in Cumhuriyet on alleged arms smuggling to Syrian rebels. The verdict is being appealed. Dündar left Turkey after the coup attempt, saying he would not receive a fair trial.