The pro-Kurdish HDP party in Turkey has denounced the arrest of its leaders as an attempt by the government to eradicate democracy, BBC News reports.

The HDP said the arrests were a dark day for the country, as its supporters took to the streets in protest.

HDP joint leaders Selahattin Demirtas and Figen Yuksekdag are accused of spreading propaganda for militants fighting the Turkish state.

They and 10 other HDP activists deny links to the PKK Kurdish rebel group.

All were arrested for refusing to answer prosecutors' questions.

Demirtas has won international support with his liberal politics, but critics say he has failed to distance the party sufficiently from the PKK.

Hours after the arrest, a huge car bomb killed eight people and wounded more than 100 in the south-eastern city of Diyarbakir.

Turkish authorities blamed the outlawed PKK (Kurdistan Workers' Party), but the group known as Islamic State later claimed the attack through its Amaq news agency.