Some 60 Turkish writers, publishers and journalists currently face prosecution or are incarcerated, including 19 jailed reporters, Alexis Krikorian of the Geneva-based International Publishers Association (IPA), said on Tuesday.
"This is way more than anywhere else in Europe or Central Asia. This indicates a sustained freedom of expression problem," Krikorian said.
Authorities banned 15 books in the first half of last year for raising sensitive issues like the treatment of minorities or the role of the powerful military, he said.
"We welcome the legislative reforms that have been passed recently. At the same time we have repeatedly called on the authorities to stop harassing writers and publishers who refuse self-censorship and to implement these reforms," Krikorian said.
Turkey's recent reforms aimed at broadening human rights helped to convince European leaders in December to agree to start membership talks with the long-standing aspirant.
But many of the political changes remain on paper and Turkey lacks the democratic spirit behind the reforms, Eugene Schoulgin of International PEN, a writers' advocacy group, said.
"Although the Turkish state has decided to amend some articles because it wants to join the European Union, the mentality in this country has not changed," he said.
"We have repeatedly called on the authorities to stop harassing writers and publishers who refuse self-censorship"
International Publishers Association (IPA)
"As long as this goes on, Turkey will not have a chance of being accepted as a member of the community."
The EU has said Turkey's prosecution of journalists remains a cause of concern, despite a recent overhaul of its penal code.
Krikorian and Schoulgin were part of a delegation that included representatives from Amnesty International and Human Rights Watch in Turkey to observe two trials on Wednesday.
Fikret Baskaya, an economics professor, is charged with "insulting" the military and faces three years in prison for articles he wrote in the early 1990s about a possible government hand in an arson attack that killed 38 people.
Publisher Ragip Zarakolu is accused of "inciting hatred" for publishing a magazine containing criticism of the state's treatment of Kurds. He faces two years in jail if convicted.
"They face trial because they used their right of free expression. They are being treated as terrorists or criminals ... and this is unacceptable," Krikorian said.