The UN voiced alarm on Tuesday at Turkey’s use of mass detentions amid countrywide demonstrations over the arrest of Istanbul’s popular opposition mayor, urging authorities to investigate alleged unlawful use of force against protestors.

“We are very concerned by the detention of at least 92 people by the Turkish authorities over the past week,” United Nations rights office spokeswoman Liz Throssell said in a statement.

She emphasized in particular the arrest of President Recep Tayyip Erdogan’s main political rival, “Ekrem Imamoglu, Istanbul’s democratically elected mayor, who is facing corruption charges and has been removed from office.”

Since his arrest, huge crowds have hit the streets daily, prompting nightly clashes with riot police that have spread across the country.

More than 1,400 people have been arrested in connection with the mass protests, Interior Minister Ali Yerlikaya said on Tuesday.

The “country-wide demonstrations … were met with unlawful blanket bans on protests in three cities,” Throssell said, also stating that “at least nine media workers” were among those arrested.

A Turkish court on Tuesday remanded into custody seven journalists for covering the protests, including AFP photographer Yasin Akgul, who was seen being escorted to jail.

Press freedom group Reporters Without Borders (RSF) denounced the move as “scandalous.”

“All those detained for the legitimate exercise of their rights must be released immediately and unconditionally,” Throssell said, while those facing charges must be accorded “due process and fair trial, including access to a lawyer of their own choice.”

The UN rights office, she added, wanted allegations of unlawful use of force by police against protesters be “promptly and thoroughly investigated.”