Prosecutors have launched investigations into the academics on possible charges of insulting the state and engaging in "terrorist propaganda" on behalf of the outlawed Kurdistan Workers' Party, or PKK.

The state-run Anadolu Agency reported that 15 academics from Kocaeli University in northwestern Turkey and three from Uludag University in the neighboring province of Bursa were detained for questioning on Friday. Chief Prosecutor Mustafa Kucuk accused the group of spreading terrorist propaganda and "insulting the moral integrity of the state." Prime Minister Ahmet Davutoglu implied the academics had chosen to "align" themselves with terrorists.

On Friday, students protested the arrests under the banner "don't touch my teacher."

In an open letter to President Recep Tayyip Erdogan published last month, the academics wrote: “We demand the state abandon its deliberate massacre and deportation of Kurdish and other peoples in the region. We also demand the state lift the curfew, punish those who are responsible for human rights violations, and compensate those citizens who have experienced material and psychological damage. For this purpose, we demand that independent national and international observers to be given access to the region and that they are allowed to monitor and report on the incidents.”

Presidential response

Among those who signed the declaration was US academic Noam Chomsky.

After the bomb attack on a tourist area of Istanbul earlier this week, Erdogan criticized Chomsky and the other academics, saying on Friday: "Just because they have titles such as professor, doctor in front of their names does not make them enlightened. These are dark people," Erdogan said. "They are villain and vile because those who side with the villain are villain themselves."

Erdogan invited Chomsky to visit the area but he rejected the offer and wrote to the UK's Guardian newspaper saying: "If I decide to go to Turkey, it will not be on his invitation, but as frequently before at the invitation of the many courageous dissidents, including Kurds who have been under severe attack for many years."

Chomsky also accused Erdogan of hypocrisy saying: "Turkey blamed Isis [for the attack on Istanbul], which Erdogan has been aiding in many ways, while also supporting the al-Nusra Front, which is hardly different. He then launched a tirade against those who condemn his crimes against Kurds, who happen to be the main ground force opposing Isis in both Syria and Iraq."

Signatories doubled

Organizers of the declaration say that the number of signatories to it has doubled in the last month.

The move against the academics has been criticized by the largest opposition group in parliament, the People's Republican Party (CHP) who said the criminal proceedings against the academics were "unlawful, not acceptable and extremely dangerous."

The US Embassy in Ankara also expressed concern over the detentions and a "chilling effect" on political discourse. "Expressions of concerns about violence do not equal support for terrorism," Ambassador John Bass said in a statement. "Cricism of the government does not equal treason."

The arrests come a day after an attack on a police station in the south-east, blamed on PKK militants.

jm/jil (AFP, dpa, AP)