The New York-based media watchdog wrote to Turkish Prime Minister Recep Tayyip Erdogan to condemn the arrests as well as the media repression "that has earned Turkey a reputation as one of the world's worst press freedom violators and done grave damage to the consolidation of Turkish democracy."

Of the 40 individuals arrested in coordinated raids across the country, CPJ "has been able to identify 29 journalists by name and affiliation, and it continues to examine 11 others," read the letter, signed by CPJ director Joel Simon.

On December 20 Turkish police arrested several journalists, including AFP photographer Mustafa Ozer, in an operation against people with suspected links with Kurdish rebels.

Ozer was arrested after his house in Istanbul was searched for several hours by anti-terror police, who also seized CDs and documents and copied memory cards, lawyer Sibel Tokaoglu told AFP.

"Your government claims that the operation targets 'the press and propaganda' arm of the Union of Kurdistan Communities (KCK), but it provides no evidence supporting this assertion," Simon wrote.

The government claims the KCK is the urban wing of the Kurdistan Workers' Party (PKK), which is listed as a terrorist organization by Turkey and much of the international community.

The PKK took up arms for Kurdish independence in southeastern Turkey in 1984, sparking a conflict that has claimed some 45,000 lives.

"We are even more deeply troubled" by the arrests "because some in the Turkish media have alleged that a recent CPJ report confirming that eight Turkish journalist have been jailed for their work may have emboldened your government to take action."

"It would be perverse for your government," the letter read, "to take any solace" that journalists have been jailed for their work.

That number "places Turkey firmly in the company of some of the world's most repressive countries and deeply compromises your government's commitments to democracy and the rule of the law."

The group said it intends to send a delegation to Turkey next year "to further review the outstanding cases," and urged the Turkish government to cooperate.

Since 2009, 700 people have been arrested for alleged links with the rebels, according to the government, but the pro-Kurdish Peace and Democracy Party (BDP) puts the figure at more than 3,500.