Istanbul Mayor Ekrem Imamoglu has arrived at prison after a Turkish court formally placed him under arrest pending trial on corruption charges, days after his detention triggered mass protests across the country.

Imamoglu arrived at Marmara Prison on Sunday near Istanbul’s Silivri district. He has called for more nationwide protests.

The court on Sunday said Imamoglu and at least 20 others were jailed as part of a corruption investigation. The court in Istanbul did not press “terror” charges against the 53-year-old jailed mayor.

“Although there is strong suspicion of aiding an armed terrorist organisation, since it has already been decided that he will be arrested for financial crimes, (his arrest) is not deemed necessary at this stage,” it said.

Later Sunday, the Interior Ministry said Imamoglu has been removed from mayoral duty after his formal arrest and jailing.

Al Jazeera’s Sinem Koseoglu, reporting from Istanbul, said several others who were charged were ordered released, pending trial.

Since “terror” charges were not slapped on Imamoglu, the court will not be able to appoint a government trustee to the municipality of Istanbul, the country’s largest city. The mayor would be elected from within the municipal council, Koseoglu said.

“It is good news for the main opposition party [Republican People’s Party (CHP)], which controls a majority in the municipal council,” she added.

‘Not bow down’

In his first response after the court ruling, Imamoglu said he will not bow down.

“We will, hand in hand, uproot this blow, this black stain on our democracy… I am standing tall, I will not bow down,” the Istanbul mayor said in a post on X.

In another post, Imamoglu said the legal process over his detention was “a complete extrajudicial execution” which meant a “betrayal against Turkiye”. He called on Turks to hold mass demonstrations across the country against his arrest.

CHP leader Ozgur Ozel told reporters the party would file legal appeals against the court ruling. He said the Istanbul municipality council would now elect someone to work as acting mayor while it awaits a ruling on Imamoglu.

The mayor, a key opposition figure and potential challenger to longtime President Recep Tayyip Erdogan, was detained on Wednesday by the government over alleged corruption and terrorism.

Imamoglu has denied all charges, describing them as part of a “smear campaign”.

Ankara Mayor Mansur Yavas, an ally of Imamoglu, told reporters that the jailing is a disgrace to the judicial system.

The court’s decision to send Imamoglu to pre-trial detention comes after the opposition, European leaders and tens of thousands of protesters criticised the actions against him as politicised.

The government has denied the cases are politically motivated.

President Erdogan on Saturday accused the CHP’s leadership of turning the party “into an apparatus to absolve a handful of municipal robbers who have become blinded by money”.

He also accused it of “doing everything to disturb the public peace, to polarize the nation”.

“Despite a protest ban, which was extended until March 26, demonstrations have been going on, including in Istanbul, Ankara and about 50 other cities last night.”

Police said at least 300,000 people protested in Istanbul on Saturday night. However, the opposition claimed the number was close to one million. Al Jazeera could not verify the latter number.

The court decision on Sunday also comes as opposition CHP members and others head to polling stations for a primary election to choose a candidate for the next presidential election in 2028.

Imamoglu is likely to be chosen as CHP’s candidate, but his plans to stand in the next election were hurt after Istanbul University annulled his diploma last week, citing irregularities with Council of Higher Education regulations. Under the Turkish constitution, presidential candidates must have a higher education degree.

The CHP has called for non-party members to vote in order to boost public resistance after Imamoglu’s detention.

CHP, which has more than 1.5 million members, set up 5,600 ballot boxes for voting across all of Turkiye’s 81 provinces. Polls will close at 14:00 GMT.