Turkish courts on Friday formally arrested the two co-leaders of the pro-Kurdish Peoples' Democratic Party (HDP) as well as seven more of the party's MPs, state-run Anadolu news agency said.

Party leaders Selahattin Demirtas and Figen Yuksekdag, who were detained overnight during a terror investigation, were on Friday remanded in custody by a court in the southeastern city of Diyarbakir.

They will be held behind bars pending trial, although no date has been set yet. 

A total of 12 HDP parliamentarians were rounded up overnight in an unprecedented crackdown on the party, which has sparked international alarm.

As well as Demirtas and Yuksekdag, seven other MPs were also remanded in custody following hearings in Diyarbakir and in other cities.

Among them were Idris Baluken, head of HDP's parliamentary faction, and six other parliamentarians -- Leyla Birlik, Nursel Aydogan, Selma Irmak, Gulser Yildirim, Ferhat Encu and Abdullah Zeydan.

Another three HDP lawmakers -- Ziya Pir, Imam Tascier and Sirri Sureyya Onder -- were allowed to go free under judicial control, the Turkish equivalent of bail.

The arrest rulings for Encu and Zeydan were announced late in the evening, meaning all 12 of those rounded up overnight had either been freed or remanded in custody within a single day.

However, one more wanted HDP MP, Tugba Hezer Ozturk, is currently abroad and efforts are under way to find another, Nihat Akdogan, who is believed to be in Turkey but has so far evaded detention, Anadolu said.

Source: AFP