ISTANBUL – A court formally arrested the mayor of Istanbul and key rival to President Recep Tayyip Erdogan on Sunday and ordered him jailed pending the outcome of a trial on corruption charges.

Mayor Ekrem Imamoglu was detained following a raid on his residence earlier this week, sparking the largest wave of street demonstrations in Turkey in more than a decade. It also deepened concerns over democracy and rule of law in Turkey.

His imprisonment is widely regarded as a political move to remove a major contender from the next presidential race, currently scheduled for 2028.

Government officials reject accusations that legal actions against opposition figures are politically motivated and insist that Turkey’s courts operate independently.

The formal arrest came as his opposition Republican People’s Party, or CHP, began holding a primary presidential election to endorse Imamoglu as its presidential candidate despite the arrest.

The party has also set up symbolic ballot boxes nationwide — called “solidarity boxes” — to allow people who are not party members to express their support to the mayor.

The mayor’s arrest marks an escalation of a government crackdown on opposition figures and dissenting voices.

Before his detention, Imamoglu had already faced multiple criminal cases that could result in prison sentences and a political ban. He was also appealing a 2022 conviction for insulting members of Turkey’s Supreme Electoral Council.

Earlier in the week, a university nullified his diploma, citing alleged irregularities in his transfer from a private university in northern Cyprus some 30 years ago. The decision effectively bars him from running for president, since the position requires candidates to be university graduates. Imamoglu had vowed to challenge the decision.

Imamoglu was elected mayor of Turkey’s largest city in March 2019, in a major blow to Erdogan and the president’s Justice and Development Party, which had controlled Istanbul for a quarter-century. Erdogan’s party pushed to void the municipal election results in the city of 16 million, alleging irregularities.

The challenge resulted in a repeat of the election a few months later, which Imamoglu also won.

The mayor retained his seat following local elections last year, during which the CHP made significant gains against Erdogan’s governing party.