Turkish police have raided the premises of a business and media conglomerate linked to a prominent opposition figure whom the government accuses of trying to destabilise it.

Authorities in the capital Ankara searched 23 companies belonging to Koza Ipek Holding on Tuesday over suspicion of funding a movement led by the Islamic cleric Fethullah Gulen, who is based in the US, the state-run Anadolu Agency reported.

Six people were detained, according to Anadolu, but there was no immediate comment from the police.

Koza Ipek Holding owns opposition television stations Bugun TV and Kanal Turk, as well as the Bugun newspaper, among other business interests.

Yavuz Baydar, a Bugun columnist, told Al Jazeera that the police first raided Koza Ipek Holding's headquarters, before the operation "spread out to the offices of Kanal Turk and Bugun".

He said it was the latest episode of the of government's media crackdown and noted that it came "about 12 hours after two UK journalists working for Vice News and their fixer were detained" and charged with being members of ISIL.


Related: Vice News staff in Turkey charged as being ISIL members


Critics denounced Tuesday's operations as a crackdown on opposition voices ahead of a snap election on November 1.

Hundreds of demonstrators responded by staging protests outside Koza Ipek firms against the police raids.

"I hope those who rule this country will come back to democracy and justice as soon as possible before these [raids] begin damaging our society, country and our nation," Ahmet Gursoy, a protester, said.

They are wrong if they think they can silence people by heaping pressure on innocent people, media outlets and businessmen." 

'Muzzling dissent'

Kemal Kilicdaroglu, leader of the country's main opposition party, called the police operation an attempt to muzzle dissent.

"We cannot speak of democracy in a country where the media is being silenced," he said.

Koza Ipek Holdings is associated with Gulen's movement, which the government accuses of orchestrating a vast corruption scandal in 2013 with the aim of toppling the government.

Gulen has rejected accusations that he was behind the scandal that implicated President Recep Tayyip Erdogan's close associates.

The government has dismissed the allegations as an attempted coup.

Hundreds of police and judiciary officials suspected of ties to Gulen's movement have been dismissed. In May, Turkey's banking regulator seized a bank associated with the movement.

In December 2014, police arrested more than two dozen senior journalists and media executives allegedly tied to the Gulen movement on various charges.

A statement by the US state department cautioned Turkey not to violate its "own democratic foundations" while drawing attention to raids against media outlets "openly critical of the current Turkish government".

Source: Al Jazeera and agencies