The co-chairs of the opposition Peoples' Democratic Party (HDP) were arrested on Friday for failing to answer a counter-terrorism investigation summons, a judicial source said.
Party co-leaders Figen Yuksekdag and Selahattin Demirtas and parliamentary group leader Idris Baluken were among 12 deputies arrested by police after prosecutors in Turkey's east and southeast approved the arrests, the Interior Ministry said in a statement earlier.
The detentions were carried out across Diyarbakir, Hakkari, Van, Sirnak and Bingol provinces.
Yuksekdag and Demirtas, who vowed in June not to testify, as well as lawmaker Sirri Sureyya Onder were earlier Friday referred to a court in Diyarbakir for a judge to assess the prosecution case, a security official said on condition of anonymity.
Baluken was taken to court in Bingol. He was remanded in custody.
HDP's Diyarbakir lawmaker Nursel Aydogan and Sirnak lawmaker Leyla Birlik, who were taken to court in Sirnak, were also remanded in custody.
A further HDP lawmaker, Imam Tascier, was released under judicial control on Friday afternoon. Onder was also released under judicial control later on Friday.
In addition, the party's deputy for Mardin, Gulser Yildirim was remanded in custody by a local court in Diyarbakir.
At a press conference following a parliamentary group meeting in Ankara, HDP spokesman Ayhan Bilgen criticized the arrests, saying they were "not legal" but "political".
The lawmakers face prosecution under anti-terrorism laws after their parliamentary immunity was lifted earlier this year.
Lawmakers from other parties also face a range of investigations but only HDP deputies have refused to testify before prosecutors.
Among the charges facing the HDP lawmakers are offenses of spreading terrorist propaganda in relation to comments made in October 2014, after Daesh militants entered the Syrian border town of Kobani, also known as Ayn Al-Arab.
Demirtas and other HDP figures had urged citizens to take to the streets. The ensuing week of violent demonstrations left dozens dead, including two police officers, and saw hundreds of people injured.
The government has accused the HDP of having links to the PKK, which is listed as a terrorist organization by Turkey, the EU and U.S.
Other HDP deputies arrested included Ferhat Encu, Selma Irmak, Abdullah Zeydan, and Ziya Pir.
Pir was later released after being sent to court in Diyarbakir. He is under investigation on charges of making "terrorist group propaganda and praising crimes and criminals".
Three other HDP deputies are at large, including two believed to be overseas.
Protests erupted across Turkey during the Eid al-Adha holiday on October 6, 2014, a day after Daesh entered the Syrian border town of Kobani.
The protests occurred after Demirtas had urged citizens to take to the streets.
The ensuing week of violent street demonstrations and clashes across Turkey left dozens of people dead, including two police officers, and hundreds injured.
Other HDP members detained Friday include HDP's parliamentary leader Idris Baluken, Ferhat Encu, Leyla Birlik, Selma Irmak, Abdullah Zeydan, Sirri Sureyya Onder, Ziya Pir, Gulser Yildirim and Nursel Aydogan.
The interior ministry said in a statement that two more MPs were being sought and two others were abroad.
The HDP's headquarters in Ankara was also raided by police Friday night. HDP currently holds 59 chairs in the parliament as the third largest party in Turkey.