ANKARA, Turkey (AP) — Turkish authorities on Tuesday detained a former mayor and dozens of municipality officials in the western city of Izmir over alleged corruption, extending a crackdown against the country’s main opposition party.

Police detained 120 officials from the opposition Republican People’s Party, or CHP, including former Izmir Mayor Tunc Soyer and the party’s provincial leader Senol Aslanoglu, state-run Anadolu Agency said. In total, the Izmir Public Prosecutor’s Office issued arrest warrants against 157 officials as part of an investigation into alleged rigging of municipality tenders and fraud, it added.

Officials from CHP-controlled municipalities in Istanbul and elsewhere have faced waves of arrests this year, including Istanbul’s Mayor Ekrem Imamoglu who was arrested in March over allegations of corruption. His arrest triggered the largest street protests Turkey has seen in more than a decade.

Imamoglu is regarded as the main challenger to President Recep Tayyip Erdogan's 22-year rule and was officially nominated as his party’s presidential candidate following his imprisonment. Turkey’s next election is due in 2028 but could come sooner.

Many people in Turkey consider the cases to be politically driven, according to opinion polls. But Erdogan’s government insists the courts are impartial and free from political involvement.

The crackdown comes a year after the CHP made significant gains in local elections.