Turkish authorities detained five suspects on bribery and money laundering charges as part of an investigation targeting Istanbul’s Beşiktaş Municipality, the Istanbul Chief Public Prosecutor’s Office announced Tuesday.

In a statement, prosecutors said the investigation was being carried out in coordination with the Istanbul Police Department’s Financial Crimes Unit.

Among those detained were former Beşiktaş Deputy Mayor Cevdet Çalı and current municipal council member İlker Uluer of the main opposition Republican People’s Party (CHP). Former CHP municipal council member Oylum Işık was also among the suspects taken into custody.

The other suspects were identified as Beşiktaş Municipality Personnel Services Manager Bülent Karakaş and Sarbel Organization office employee Özlem Demir Karakaş.

Authorities said searches conducted at the suspects’ homes and offices led to the seizure of numerous digital materials, along with $90,000 (TL 4.1 million) and 5,000 euros ($5,809) believed to be proceeds of crime.

The investigation is ongoing.

The main opposition CHP is under mounting scrutiny as a wave of corruption, bribery and terrorism-related investigations sweeps across its municipalities, with dozens detained in coordinated raids across several cities.

More than 20 mayors governing CHP municipalities were detained or arrested in the past two years on charges of corruption, along with dozens of municipal bureaucrats in Istanbul, Antalya, Bursa, Bolu and Uşak.

High-profile cases include Istanbul’s suspended mayor, Ekrem Imamoğlu, and Antalya’s ousted mayor, Muhittin Böcek, whose cases have drawn national attention following their arrests late last year and trials that began earlier this month.