The UN called Friday on Egyptian authorities to "radically change their approach" to any future protests, after reports of widespread arrests following demonstrations last weekend against President Abdel Fattah al-Sisi.
The UN rights chief Michelle Bachelet expressed deep concern over reports that thousands of people, including lawyers, rights defenders, political activists and journalists, were arrested in connection with the September 20-21 protests.
"I urge the authorities to radically change their approach to any future protests, including those that may take place today," Bachelet said in a statement, as the country braces for a possible new round of weekend demonstrations.
"All those arrested and detained solely for exercising their rights should be released immediately," she insisted.
Last week's open defiance of Sisi -- triggered by viral videos from exiled Egyptian businessman Mohamed Aly -- has surprised observers in a country where opposition of all stripes has been severely curtailed.
Elected president in 2014 after ousting predecessor Mohamed Morsi and his Muslim Brotherhood the previous year, Sisi is seen by many as one of the most authoritarian figures in the Middle East.
In recent days, security has been visibly stepped up, especially in Cairo's Tahrir Square -- the epicentre of the 2011 popular revolt that toppled long-time autocrat Hosni Mubarak.
Alongside beefing up their presence on the streets, the security forces have also detained people they suspect of being key influencers of unrest -- journalists, human rights activists and lawyers.
The UN rights office said it had been informed that a number of those detained before, during and after last weekend's protests were subsequently released.
But it voiced alarm at reports that some of those detained were denied legal representation when appearing before the public prosecutor, and some had allegedly been charged with serious offences, including aiding a terrorist group and spreading "false news".
"I remind the Egyptian government that under international law people have a right to protest peacefully," Bachelet said.
"They also have a right to express their opinions, including on social media," she said, urging Egyptian authorities to follow international norms and to respect the right to freedom of expression and peaceful assembly.
People "should never be detained, let alone charged with serious offences, simply for exercising those rights," she stressed.
