Istanbul - Turkish police on Friday detained at least 18 academics who signed a petition criticising a military crackdown in the Kurdish-dominated southeast, triggering new alarm about freedom of expression in the country.
In a rare rebuke to Washington's NATO ally, the US ambassador to Turkey expressed alarm over the investigations, with Western concern on freedom of expression already riding high due to the detention since November 26 of two prominent opposition journalists.
They were arrested in raids targeting 21 academics accused of disseminating "terrorist propaganda" by signing a petition denouncing military operations against Kurdish rebels.
Fifteen academics and lecturers from the University of Kocaeli, near Istanbul, were initially detained, with another three academics from Uludag University in western Bursa province later held in their offices, Dogan news agency said.
The academics were questioned for a day before being released, Dogan reported late Friday.
Prosecutors on Thursday launched a vast investigation into over 1,200 academics from 90 Turkish universities for engaging in "terrorist propaganda" and "inciting hatred and enmity" by signing the petition.
Entitled "We won't be a party to this crime", the petition urged Ankara to halt "its deliberate massacres and deportation of Kurdish and other peoples in the region", angering President Recep Tayyip Erdogan.
Turkey is waging an all-out offensive against the separatist Kurdistan Workers' Party (PKK), with military operations backed by curfews aimed at flushing out rebels from several southeastern urban centres.
But Kurdish activists say dozens of civilians have died as a result of excessive force and the operations have become the subject of huge controversy in Turkish society.
Erdogan on Friday launched his strongest attack yet on the signatories, accusing them of supporting the Kurdish rebels and thus being a "party" to the crimes of the PKK.
"Those standing by the perpetrators of the massacres are a party to the crime," he told reporters after Friday prayers in Istanbul.
"Our people must understand who is who - having a PhD title doesn't necessarily make you an intellectual. These are people in the dark. They are cruel and despicable." Critics have denounced the move as the latest attempt by Erdogan to stifle dissent, with the pro-Kurdish People's Democratic Party (HDP) condemning "the steps taken by the Turkish government that are plunging Turkey into a deep darkness".
"These operations... which are only seen in undemocratic regimes are very dangerous and unacceptable," the main opposition Republican People's Party (CHP) added in a statement.
US ambassador to Ankara John Bass expressed concern over the "pressure having a chilling effect on legitimate political discourse across Turkish society regarding the sources and solutions to the ongoing violence".
"In democratic societies it is imperative that citizens have the opportunity to express their view, even controversial or unpopular ones," he said in a statement.
"Expressions of concern about violence do not equal support for terrorism. Criticism of the government does not equal treason," he added.
Ankara's controversial mayor Melih Gokcek, a member of Erdogan's ruling Justice and Development Party (AKP), hit back at Bass by telling him to go home and saying he was "a wrong choice for the US in Turkey." "You are trying to make an enemy (of Turkey). At least you should learn to be quiet," he wrote on Twitter.
Universities opened internal probes into over 60 academics in at least seven cities across Turkey that could potentially lead to their dismissal, reports said.
A number of academics targeted in the probe withdrew their signatures Friday, with Kemal Inal, an associate professor of communications at the Ankara-based Gazi University, saying: "I agree that some statements in the petition are harsh." "But I'm in favour of peace, brotherhood and friendship," he said in a statement quoted by the Anatolia news agency. "We just don't want anyone to die."
The petition was also signed by dozens of foreigners, among them American linguist Noam Chomsky and the Slovenian philosopher Slavoj Zizek. They are not currently under investigation.
The US and European Union have already expressed concern over the imprisonment pending trial of the editor of the Cumhuriyet newspaper and the daily's Ankara bureau chief for publishing articles alleging the government delivered weapons to Islamists in Syria.