Egypt's prosecution service on Saturday referred 13 men to trial for alleged sex attacks on women at Cairo's Tahrir Square, including during inaugural celebrations for new President Abdel Fattah al-Sisi.
It was the first time charges have been made in the North African country in connection with mass sexual assaults.
The attacks took place on January 25, 2013, as Egypt marked the second anniversary of the 2011 revolt, and on June 3 and June 8 this year as revellers marked Sisi's election victory and inauguration, the prosecutor general's office said.
The 13 accused, including a minor, are charged with "kidnapping, raping, sexually attacking, attempting to murder and torturing the women", it said.
If convicted of the charges, the defendants could be sentenced to life imprisonment.
Since the uprising that toppled long-time president Hosni Mubarak in 2011, the problem of sexual harassment has worsened in Egypt, with women regularly attacked during rallies by groups of men in and around Tahrir Square, the epicentre of protests.
Hundreds of women protested in Cairo on Saturday against the assaults.
Activists were outraged this week after graphic video footage of a woman being sexually assaulted at Tahrir Square went viral on YouTube, Facebook and Twitter.
The footage, apparently filmed using a mobile phone, shows a mob of men surrounding a young woman, who was stripped and badly bruised in the assault.
It was unclear whether the victim in the video was among those attacked during the pro-Sisi celebrations.
The prosecution service said police were searching for the person who recorded the video as this action was against "public morals".
Egypt, which had no specific law on sexual harassment, only recently approved penalties for such offences to include jail terms, fines or both.
- 'Death to attackers'-
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The prosecution service described the June 3 and 8 Tahrir attacks during the pro-Sisi celebrations.
"Two groups of criminals went to the square and caught a woman and her daughter. They took the woman to an area near a mosque close to the square where she was attacked and stripped of her clothes," it said of the June 3 assault.
"They beat her and when she tried to escape, hot water fell on her causing serious burn injuries. Despite this the attackers circled her and sexually attacked her until she was rescued by police and citizens."
Three people were arrested in connection with this attack.
On June 8, several women aged between 17 and 42 were attacked at the square by members of the same mob who carried out the June 3 assault, the prosecution said.
"The attackers separated the women, took them to different spots in the square and circled them. They then attacked the women, beat them and even threatened to kidnap the children of one of the victims," it charged.
The victims were later rescued by police and others. Eight men were arrested over this assault.
Two other men have been arrested for an attack which took place on January 25 last year.
The prosecution said two men have also been detained for sexually harassing two girls in Cairo's Heliopolis district but they were still to be referred to trial.
Several hundred women demonstrated in Cairo on Saturday against the assaults.
"People demand death for attackers," they chanted, with some carrying placards saying "Don't tell me how to dress, tell them not to rape!"
"A sexual attack damages a woman not just psychologically, but destroys her self-esteem. The attacker deserves only death penalty," one protester told AFP.
Human Rights Watch said such attacks "marred" Sisi's election and inauguration.
"Egypt’s women, and the world, are watching to see what President Sisi will do to put a halt to the sexual attacks and harassment," an HRW statement on Friday said.
Sisi had urged YouTube to remove the video of the assault after the victim herself told him to do so when he visited her in hospital, his spokesman said on Friday.
On Saturday he said YouTube had removed scenes which could have revealed her identity.