Turkey's widespread use of anti-terrorism laws has led to criminal cases against more than 100 journalists and created a climate of fear that is undermining recent democratic reforms, a media watchdog says.
Prime Minister Tayyip Erdogan's government is also exerting "heavy pressure" on the judiciary to keep journalists in custody before and during their trials, London-based PEN International said.
The main focus of Turkey's anti-terrorism laws has been militant separatist activities, but the government has faced growing criticism from the European Union, which Turkey seeks to join, and others for applying the laws too widely.
"No situation of violence justifies a broad, badly defined anti-terror law which is used to deal not with violence but with limiting freedom of expression," John Ralston Saul, president of PEN International, said in a news conference in Istanbul.
"The current situation creates an atmosphere of uncertainty and fear which then leads to self-censorship and the limitation of freedom of expression."
Between 60 and 70 members of the press are in jail during their trials, and another 60 to 70 journalists are on trial but are not in custody, PEN said.
That compares with 800 writers, journalists, bloggers and other media workers in prison or at risk of being jailed worldwide, it said.
The trials threaten to undermine the expansion of democratic rights Erdogan ushered in during his first term in office, many aimed at meeting European Union membership criteria, Saul said.
Once hailed as a reformer by the EU and other observers, Erdogan more recently has faced accusations of taking an authoritarian approach towards his political opponents.
For his part, Erdogan has argued that the mass trials of hundreds of people, including journalists, accused of plotting to overthrow his government has helped stabilise NATO-member Turkey, which is enjoying unprecedented economic prosperity.
Most of the journalists Turkey has imprisoned are accused of links with the outlawed Kurdistan Workers Party (PKK). More than 40,000 people have been killed in the conflict between Turkey and the PKK, which launched its insurgency in 1984 and seeks greater autonomy for the country's estimated 15 million ethnic Kurds.
The PEN criticism followed last month's EU progress report on Turkey which spoke of an "increasing tendency to imprison journalists", and a report from the US-based Committee to Protect Journalists which said Erdogan's government was carrying out one of the world's biggest crackdowns against press freedom.
The number of writers, publishers and journalists prosecuted in Turkey has roughly tripled since 2010, said Sara Whyatt, PEN International's deputy director.
The PEN delegation met Turkish President Abdullah Gul, who expressed hope the situation would be resolved, Saul said.
A review of the cases involving journalists should be carried out, Saul urged. Such a process would result in most of them being dismissed, he said. "We call for an end to the pseudo-legal system that involves prolonged pre-trial detentions and dragged-out trials," he said.
Ahmet Sik, an investigative reporter who spent more than a year in prison on charges he belongs to a "terrorist group" for things he had written about the police before his release earlier this year, is still awaiting a verdict.
"In every oppressive country you silence the press to keep the people quiet," Sik said. "Things were bad in the past, but then it was the military junta. Now it's a civilian government obstructing press freedom, which is more tragic."