ISTANBUL—Turkish police on Tuesday arrested 26 journalists in a sweep a media-rights organization said was aimed at sympathizers of the outlawed Kurdish Workers’ Party, or PKK, heightening criticism of the country’s record on press freedom.

If the number is confirmed, the arrests would bring the number of journalists in Turkish jails to more than 90, one of the highest detention rates for journalists in the world, said the Bianet media-rights monitoring group.

The journalists, most of them working for Kurdish newspapers and agencies, were arrested on Tuesday as part of an operation against the Kurdistan Communities Union, or KCK, an umbrella organization for Kurdish nationalist groups that the government says acts as the urban wing of the PKK.

Agence France-Presse news agency said Mustafa Ozer, a photographer the agency employs in Turkey, was among the detained. Mr. Ozer is of Kurdish origin.
It wasn’t clear how many people were arrested on Tuesday. The state Anadolu news agency said 25 people were arrested in Istanbul, while other media put the figure at 38 nationwide.

A spokesman for the Justice Ministry declined to comment. Turkey’s government has denied repeatedly that any journalists are being held in connection with their work, but it has come under growing criticism from the European Union and Washington, as well as from international civil-rights groups, over the detentions.

Turkey’s military is engaged in a full-scale assault against the PKK, which had stepped up attacks against Turkish police and military since the beginning of the year, raising the stakes in a 30-year conflict that has left at least 30,000 people dead, according to estimates by analysts. The U.S., EU and Turkey list the PKK as a terrorist group.

"Today’s arrests are shocking and worrying. They are directed at the pro-Kurdish opposition press. In a democratic society, such a crackdown on opposition journalists is very worrying and puts Turkey’s international credibility into doubt," said Emma Sinclair-Webb, a Human Rights Watch researcher working in Turkey.
"The aim is to make censorship and self-censorship an inseparable part of journalism," the Turkish Journalists Association said late Tuesday that condemned the arrests as a sign of "heavy pressure" against opposition media.

Most of the journalists have been arrested under Turkey’s sweeping antiterrorism laws, which allow suspects to be held for years while awaiting trial on grounds that they abetted terrorists by spreading propaganda on their behalf.

Bianet said 68 journalists were in Turkish prisons before Tuesday’s arrests, either serving sentences or awaiting trial. Many are ethnic Kurds, while some are charged with aiding an alleged terrorist conspiracy that prosecutors say is known as Ergenekon to topple the government.

In a trial this month, Ilkem Ezgi Asam, a reporter for the left-wing Birgun daily, was sentenced to a year in jail for a quote she used in an article that the court said set up "officials on antiterror duties as targets."

Meanwhile, Turkish police and prosecutors have sought to crack down on the KCK, arresting lawyers, elected officials, university professors and journalists, among others. According to the Human Rights Association, a Turkish nonprofit group, 4,800 people have been arrested in the KCK operation over the past seven months, with more than 2,000 of those remaining in custody.

Among the lawyers detained were several who represent the PKK’s jailed leader, Abdullah Ocalan.