A court formally arrested the mayor of Istanbul, a 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 the accusations and insist that Turkey’s courts operate independently.

The prosecutor’s office said the court decided to jail Imamoglu on suspicion of running a criminal organization, accepting bribes, extortion, illegally recording personal data and bid-rigging. A request for him to be imprisoned on terror-related charges was rejected although he still faces prosecution. Following the court’s ruling, Imamoglu was transferred to Silivri prison, west of Istanbul.

The Interior Ministry later announced that Imamoglu had been suspended from duty as a “temporary measure.” The municipality had previously appointed an acting mayor from its governing council.

Alongside Imamoglu, 47 other people were also jailed pending trial, including a key aide and two district mayors from Istanbul, one of whom was replaced with a government appointee. A further 44 suspects were released under judicial control.

Interior Minister Ali Yerlikaya said Sunday that 323 people were detained the previous evening over disturbances at protests.

Largely peaceful protests across Turkey have seen hundreds of thousands come out in support of Imamoglu. However, there has been some violence, with police deploying water cannons, tear gas, pepper spray and firing plastic pellets at protesters in Istanbul, Ankara and Izmir, some of whom hurled stones, fireworks and other missiles at riot police.

The formal arrest came as more than 1.5 million members of the opposition Republican People’s Party, or CHP, began holding a primary presidential election to endorse Imamoglu, the sole candidate.

The party has also set up symbolic ballot boxes nationwide to allow people who are not party members to express their support for the mayor. Large crowds gathered early Sunday to cast a “solidarity ballot.”

“This is no longer just a problem of the Republican People’s Party, but a problem of Turkish democracy,” Fusun Erben, 69, said at a polling station in Istanbul’s Kadikoy district. “We do not accept our rights being so easily usurped. We will fight until the end.”

Speaking at a polling station in Bodrum, western Turkey, engineer Mehmet Dayanc, 38, said he feared that “in the end we’ll be like Russia, a country without an opposition, where only a single man participates in elections.”

In a message posted on social media, Imamoglu called on people to show “their struggle for democracy and justice to the entire world” at the ballot box. He warned Erdogan that he would be defeated by “our righteousness, our courage, our humility, our smiling face.”

“Honestly, we are embarrassed in the name of our legal system,” Ankara Mayor Mansur Yavas, a fellow member of Imamoglu’s CHP, told reporters after casting his vote, criticizing the lack of confidentiality in the proceedings.

CHP leader Ozgur Ozel said Imamoglu’s imprisonment was reminiscent of “Italian mafia methods.” Speaking at Istanbul City Hall, he added: “Imamoglu is on the one hand in prison and on the other hand on the way to the presidency.”

The Council of Europe, which focuses on promoting human rights and democracy, slammed the decision and demanded Imamoglu’s immediate release.