Four mayors from Turkey’s main pro-Kurdish opposition party were detained today as part of a “counter-terrorism” operation, the party said.

The mayors are from four towns in Turkey’s majority-Kurdish southeast—Hakkari, Yuksekova, Ercis and Nusaybin—and all members of the Peoples’ Democratic Party (HDP).

State news agency Anadolu said they were taken as part of “counter-terrorism” investigations for alleged ties to the outlawed Kurdistan Workers Party (PKK), which has fought a bloody insurgency against the Turkish state since 1984. Six other municipal officials were also arrested, Anadolu said.

Dozens of criminal cases have been opened against people around the country for criticising Turkey’s military operation against Kurdish militants in Syria since it was launched a week ago.

Among them were the co-presidents of the HDP, Sezai Temelli et Pervin Buldan, accused of “terrorist propaganda” for statements against the offensive.

The government of President Recep Tayyip Erdogan has frequently accused the HDP of being a political front for the PKK, and has periodically cracked down on the party.

Its co-founder Selahattin Demirtas has been in jail since November 2016, and several of its mayors have been removed from their posts over alleged PKK ties.