The mayors of the big southern cities of Adana and Adiyaman were detained on allegations of extortion, the Istanbul chief prosecutor’s office said, along with some eight other people.

Broadcaster NTV said Antalya’s mayor and the deputy mayor of Istanbul’s Buyukcekmece district were also detained as part of the broader investigation in which hundreds of members of the Republic People’s Party (CHP), including 11 mayors previously, have been targeted since October last year.

The CHP broadly denies the charges and calls the probe politically driven, charges the government denies.

In March, Istanbul Mayor Ekrem Imamoglu, the main political rival of President Tayyip Erdogan, was jailed pending trial on corruption charges, which he denies.

That sparked the largest street protests in a decade and a sharp selloff in Turkish assets.