Turkey's President Recep Tayyip Erdogan has warned the main opposition against "street terror" as protests against the arrest of Istanbul's mayor went on for a third day.
Mayor Ekrem Imamoglu was arrested on Wednesday over alleged corruption and aiding terrorist groups. Several other prominent figures, including two district mayors, were also held.
Mr Imamoglu can be detained for four days without charge and he was expected to be transferred to a courthouse on Saturday evening for questioning by prosecutors.
Cumhuriyet newspaper and other media reported that police began questioning Mr Imamoglu, Mr Erdogan's main political rival, on Friday afternoon. He was arrested just days before he was set to be nominated as the Republican People's Party (CHP) presidential candidate for Turkey's next elections.
Protests against the mayor's arrest have been growing since Wednesday, with the leader of the CHP calling on supporters to take to the streets for peaceful demonstrations directly against a five-day ban on protests from Turkish authorities in capital Ankara as well as Istanbul and Izmir. They are the largest protests since 2013, when Turkey was rocked by mass anti-government demonstrations that left eight people dead.

“I invite tens of thousands, hundreds of thousands, and millions to peacefully demonstrate, express our democratic reaction, and exercise our constitutional rights,” the leader of Turkey’s main opposition party, Ozgur Ozel, said.
“To those who say that calling people to the streets is irresponsible, I say this: We are not the ones filling these streets and squares," he said. "It is your lawlessness and injustices that have brought people out.”
On Thursday evening, a large protest at Ankara’s Middle East Technical University led to clashes between demonstrators and police. Students said rubber bullets were used, but the government denied that. The Interior Ministry said that more than 50 people were detained and 16 police officers were injured in the fray.
Mr Erdogan said that the government would not tolerate street protests and accused the opposition party of being associated with corruption, marginal groups and terrorist organisations.
“We see that an anti-corruption operation in Istanbul is being used as an excuse to stir unrest in our streets. I want it to be known that we will not allow a handful of opportunists to bring unrest to Turkey just to protect their plundering schemes,” Mr Erdogan said.
“Pointing to the streets instead of courtrooms to defend theft, plunder, lawlessness and fraud is a grave irresponsibility,” Mr Erdogan said. “Just as we have not surrendered to street terrorism until now, we will not bow to vandalism in the future either.”