Turkish security forces have detained at least 11 MPs from the pro-Kurdish and left-wing Peoples' Democratic Party (HDP).
Those seized include the party’s co-chairs Selahattin Demirtas and Figen Yuksekdag.
The MPs were detained on trumped-up terror charges. The Diyarbakir Chief Public Prosecutor's Office is seeking further arrests in addition to those already held.
This is a major escalation of a clampdown that has seen Kurdish and left-wing media closed down and the joint mayors of Diyarbakir arrested.
Dermirtas and Yuksekdag said, “We are elected representatives of the people. We do not represent ourselves, but the electorate. Our fight will go on.”
Access to social media sites Twitter, Facebook and Whatsapp was blocked for hours in large parts of Turkey on Friday in order to make protest more difficult.
The repressive regime of Recep Tayyip Erdogan has used July’s failed coup as an excuse to bear down on all forms of opposition. The HDP denounced the coup attempt but Erdogan thinks he can get away with the crackdown partly because other countries are seeking to use Turkey in the battles in Syria.
Turkey is still under a state of emergency imposed in July. This allows Erdogan and his cabinet to bypass parliament when drafting new laws and to restrict or suspend rights and freedoms.
Erdogan has turned away from a peace process with Kurdish groups and instead turned to brutal repression.
Despite intense attacks from the state, the HDP received more than 5 million votes, 11 percent of the total, in November 2015. This followed a breakthrough in June 2015, and the HDP is the third largest party in Turkey's parliament.
HDP supporters gathered at the party’s offices across Turkey on Friday and demonstrations have also taken place in several European cities including London.
The British-based SPOT (Solidarity with the People of Turkey) campaign says, "We are calling for an end to the state of emergency and for the release of all the arrested HDP MPs, as well as all opposition journalists, writers and academics arrested under the recent purge on opposition media outlets."