The prosecutor in Turkey's biggest city has accused popular mayor Ekrem Imamoglu of 142 corruption offences that command jail terms ranging from 828 to 2,352 years.
Imamoglu, considered the main political rival to President Recep Tayyip Erdogan, has been in pre-trial custody since March on suspicion of corruption.
The Istanbul mayor and his opposition Republican People's Party (CHP) deny any wrongdoing and accuse the president and his allies of launching a crackdown in response to Erdogan's decline in popularity.
However, the city's chief prosecutor has targeted not just Imamoglu but 401 others, with allegations of running a criminal corruption network with the mayor as its founder and leader.
After an eight-month inquiry, prosecutor Akin Gürlek stated that the suspects, of whom 105 were in detention, had formed a vast criminal organization involved in taking and receiving bribes as well as money laundering.
The estimated loss to the Turkish state is around 160 billion lira (£2.9 billion; $3.8 billion).
Imamoglu, who is the secular CHP's candidate for presidential elections in 2028, has been cited on multiple counts of bribery and fraud against public institutions.
The mayor's detention triggered widespread protests and a police crackdown since his arrest in March.
Imamoglu has also appealed against previous convictions for other charges, including insulting a prosecutor and election officials.
Party leader Özgür Özel criticized the case as a purely political maneuver to block the CHP's chances in upcoming elections, stating: His crime is to run for the next presidency of this country. He has no other crime!
