Over 1,200 academics from 90 Turkish universities calling themselves "Academicians for Peace", as well as foreign scholars, signed the petition last week calling for an end to the months-long violence.

Entitled "We won't be a party to this crime", the petition urges Ankara to "abandon its deliberate massacre and deportation of Kurdish and other peoples in the region."

It was signed by dozens of foreign luminaries and intellectuals, among them American linguist Noam Chomsky and the Slovenian philosopher Slavoj Zizek.

Istanbul prosecutors launched the investigation, with the academics facing accusations ranging from "terrorist propaganda" to "inciting people to hatred, violence and breaking the law" and "insulting Turkish institutions and the Turkish Republic," the official Anatolia news agency said.

The case has been taken up by Turkish federal prosecutors in Istanbul, with all 1,128 Turkish signatories of the petition under investigation, the Dogan news agency said.

If convicted, they could face between one and five years in prison.

Erdogan fired off an angry tirade against "those so-called intellectuals" on Thursday, accusing them of "treason" and being the "fifth columns" of foreign powers bent on undermining Turkey's national security.

"You are people in the dark. You are not intellectuals!" he said. "All you want is to stir up this country."

Erdogan first took up the issue on Tuesday when he took aim personally at Chomsky, saying that Turkey's envoy to Washington should invite the iconic cognitive scientist to see the region for himself.

Prime Minister Ahmet Davutolgu chimed in too: "It's saddening that our academics have signed such a petition when we are talking about the fight against terror."

- 'Right to free speech' -

Rights activists expressed horror that the government could not accept the petition as the result of freedom of speech.

"Turkey's PM -- himself an academic -- apparently does not recognise the right to free speech or academic freedom," Emma Sinclair-Webb, senior researcher at Human Rights Watch (HRW), wrote on Twitter.

Sedat Peker, an ultra-nationalist Turkish mafia boss, drew the ire of the opposition on Wednesday after he threatened to "shower in the blood" of all the academics who had signed the petition, in comments widely reported in the Turkish media.

Latife Akyuz, an associate professor of sociology from Duzce University in northwest Turkey, has been removed from her post after signing the petition, Dogan news agency reported.

Local prosecutors subsequently issued an arrest warrant for Akyuz for "signing a declaration legitimising or praising the violent actions of terrorist organisations," Dogan said.

Prosecutors are separately investigating signatories from two leading universities in Diyarbakir and Mardin provinces in the restive southeast, it added.

A foreign languages lecturer from Hakkari University in Hakkari, another southeastern city, has been briefly detained over the petition.

Turkey is waging an all-out offensive against the PKK, with military operations backed by curfews aimed at flushing out rebels from several southeastern urban centres.

Kurdish activists say dozens of civilians have died as a result of excessive use of force.

Six people were killed, including three children, and 39 others were wounded on Thursday in a truck bomb attack by the PKK that ripped through a police station and an adjacent housing complex for officers' families in Cinar in Diyarbakir.