The Ankara prosecutor's office on Monday said it had launched a probe against the Peoples' Democratic Party (HDP) co-leader Selahattin Demirtas over his remarks on autonomy in the southeast and "his call during October protests."
On Sunday, the HDP called for the formation of "democratic autonomous regions" in Turkey's southeast as one of its 14 items in the final declaration of the Democratic Society Congress (DTK) in Diyarbakir Province.
Demirtas will also be investigated for his alleged instigation of Kurdish protests in October 2014 over what was considered by some as the Turkish government's inaction in the advance of DAESH militants in the Syrian town of Kobani, predominantly populated by Kurds.
More than 30 people have been killed in protests across Turkey in October 2014.
The probe comes under the crimes against constitutional order statute of the Turkish Penal Code.
Earlier on Monday, Turkish Prime Minister Ahmet Davutoglu criticized the HDP over the calls for regional autonomy.