The two co-leaders of Turkey's pro-Kurdish opposition party, People's Democracy (HDP), have been detained along with at least nine other MPs.
Selahattin Demirtas and Figen Yuksekdag were detained at their respective homes as part of a counter-terrorism inquiry, security sources told Turkish media.
Hours after the arrest of Mr Demirtas in Diyarbakir, a suspected car bomb exploded there, injuring 20 people.
Diyarbakir, in the south-east, is Turkey's largest Kurdish-majority city.
Ambulances could be seen rushing to the scene amid reports of at least one death as a result of the explosion, close to a police building.
Ms Yuksekdag was detained in the capital, Ankara.
Turkey remains under a state of emergency that was imposed after a failed coup in July. The emergency allows President Recep Tayyip Erdogan and his cabinet to bypass parliament when drafting new laws and to restrict or suspend rights and freedoms.