An Istanbul court has formally arrested the city’s mayor, Ekrem İmamoğlu, on corruption charges, sending him to pre-trial detention on the day he received his party’s nomination to run for president.

The mayor of Turkey’s largest city and a rival of the president, Recep Tayyip Erdoğan, was jailed on charges of leading a criminal organisation, bribery, misconduct and corruption, along with dozens of his staff and municipal officials.

İmamoğlu and at least four others also faced a separate set of charges accusing him of “aiding an armed terrorist group” for cooperating with a leftwing political coalition before local elections last year.

Demonstrators who massed near Istanbul’s city hall, angry at the decision to officially arrest İmamoğlu, faced police who pepper-sprayed crowds. As their numbers swelled, protesters increasingly clashed with police who fired teargas. In Izmir, video showed police attempting to disperse protests using armoured water cannon trucks.

Prosecutors ruled that İmamoğlu’s detention on corruption charges alone was sufficient, despite “a strong suspicion of a crime”, opting to detain three others on terrorism charges but not the mayor. This decision is expected to allow the Republican People’s party (CHP), Turkey’s largest opposition party, to select a candidate to control the Istanbul municipality, rather than the state selecting a caretaker.

The Turkish interior ministry issued a directive to officially remove İmamoğlu and two Istanbul district mayors from office, appointing a trustee to replace one in a neighbourhood long seen as a bedrock of opposition support.

İmamoğlu has denied the accusations against him, telling investigators during questioning that his detention had “not only harmed Turkey’s international reputation but has also shattered the public’s sense of justice and trust in the economy”.

His chief spokesperson, Murat Ongun, who was also remanded in custody, posted on X: “I was arrested on slander that was not based on a single piece of evidence!”

The Istanbul mayor’s detention in a dawn raid earlier this week has sparked mass protests across Turkey, with tens of thousands taking to the streets each night and often clashing with police. The interior minister, Ali Yerlikaya, announced that 323 more people had been detained overnight as part of an investigation into the Istanbul municipality, the day after he announced that 343 people had been arrested for protesting.