Turkey detains 1,100 people since Erdogan rival's arrest
The demonstrations began in Istanbul after Ekrem Imamoglu's arrest last week and have since spread to more than 55 of Turkey's 81 provinces, sparking clashes with riot police and drawing international condemnation.
The popular 53-year-old has been widely seen as the only politician who could defeat Turkey's longtime leader Erdogan at the ballot box.
In just four days he went from being the mayor of Istanbul -- a post that launched Erdogan's political rise decades earlier -- to being arrested, interrogated, jailed and stripped of the mayorship as a result of a graft and terror probe.
On Sunday, he was overwhelmingly voted in as the main opposition CHP's candidate for the 2028 presidential run, with some 15 million people casting their ballots in a show of support for Imamoglu.
Observers said it was the looming primary that triggered the move against Imamoglu, the main political rival of Erdogan who has dominated Turkey's politics since 2003, first as prime minister and then as president.
His jailing drew sharp condemnation from Germany, which called it "totally unacceptable" as Greece said moves to undermine civil liberties "cannot be tolerated".
And the EU warned Ankara it needed to demonstrate "a clear commitment to democratic norms". Overnight, France's foreign ministry said it was a "serious attack on democracy".
'We cannot remain silent'
On Monday, students at the main universities in Istanbul and Ankara called for a boycott of lectures.
Young protesters were also preparing to hold a rally at 1400 GMT by Besiktas port on the Bosphorus, ahead of the main nightly rally outside City Hall at 1730 GMT.
Sunday night's gathering descended into fierce clashes with riot police kicking and beating people in Istanbul, AFP correspondents said.
Before dawn on Monday, police detained 10 Turkish journalists at home, including an AFP photographer, "for covering the protests", the MLSA rights group said.
Most of them were covering the mass demonstrations outside City Hall, it said, in a move denounced by Imamoglu's wife.
"What is being done to members of the press and journalists is a matter of freedom. None of us can remain silent about this," wrote Dilek Kaya Imamoglu on X.
Since Wednesday, police had detained more than 1,133 people for "illegal activities", Interior Minister Ali Yerlikaya said on Monday.
Among them were two lawyers who were defending protesters detained by the police, the Bar Association in the western coastal city of Izmir said.
Imamoglu -- who has denounced the judicial moves against him as a political "execution without trial" -- sent a defiant message from jail via his lawyers.
"I wear a white shirt that you cannot stain. I have a strong arm that you cannot twist. I won't budge an inch. I will win this war," he said.
"Out of a total of 15 million votes, 13,211,000 are solidarity votes," City Hall said, referring to the number of ballots cast by those who were not CHP members.
Faced with the massive protests, Turkey's authorities sought to shut down more than 700 accounts on X, the online platform said on Sunday.