Turkish police on Friday detained 29 people as part of an investigation into corruption allegations at Istanbul's opposition-run municipality, state media reported.
Istanbul Mayor Ekrem Imamoglu -- a key rival to President Recep Tayyip Erdogan -- has been imprisoned for over a year and is accused of running a large criminal network.
Imamoglu is currently on trial alongside 413 co-defendants. If convicted, he risks 2,430 years in prison.
Authorities have launched an investigation into the "activities of a criminal organisation established under the leadership of Ekrem Imamoglu", the state-run Anadolu news agency reported, citing a statement from the Istanbul chief prosecutor's office.
Prosecutors issued arrest warrants for 30 suspects. Twenty-nine were detained, while one remains abroad, the report said.
The suspects are accused of manipulating public tenders through a municipal subsidiary.
Imamoglu and his supporters accuse the Turkish government of doing everything to prevent him challenging Erdogan in the next presidential election, scheduled for 2028.