"Although governments have an unquestioned right to fight terrorism, it should be carried out without silencing the press and curbing the public's right to be informed," the OSCE's media representative Dunja Mijatovic said in a statement.

"This right includes reporting on sensitive issues, such as terrorism," Mijatovic said, deploring "the sheer volume of today's police raids", and warning that it "threatens the general press freedom situation."

The Organisation for Security and Cooperation in Europe (OSCE) cited news reports that some 20 journalists had been arrested over alleged links with the Kurdistan Communities Union (KCK).

Ankara claims the KCK is the urban wing of the Kurdistan Workers' Party (PKK), which is listed as a terrorist organisation 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.

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.

Around 70 journalists and intellectuals have also been arrested on various charges, including links with Kurdish rebels, provoking criticism of the Turkish authorities at home and abroad.

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