( CNN ) -- Sexual violence against female protestors at Cairo 's Tahrir Square appears to be increasing , an activist group devoted to end such assaults said Tuesday . Operation Anti-Sexual Harassment/Assault said it intervened in 15 of 19 reported sexual assaults on Friday when 10,000 people gathered in the square on the two-year anniversary of the start of the revolution that ousted President Hosni Mubarak . `` These attacks represent a startling escalation of violence against women in Tahrir Square in terms of the number of incidents and the extremity of the violence which took place , '' the group said in a news release . The organization said some of the cases involved life-threatening violence where the attackers used knives or other weapons . It said some of its members also were attacked during rescue attempts . Egyptian official warns of state 's collapse as protesters defy curfew . `` This phenomenon requires urgent attention and treatment , and is linked to the broader social problem of endemic and daily sexual harassment and assault of women , '' Operation Anti-Sexual Harassment/Assault said . U.N. High Commissioner for Human Rights Navi Pillay called for Egypt President Mohamed Morsy to do something about the assaults and other violence against demonstrators . `` It is unacceptable and a dereliction of duty not to intervene when protesters are being attacked by thugs and when women are being raped and sexually assaulted , '' she said in a written statement . The streets around Cairo 's Tahrir Square have been the sites of protests for days , including Friday 's violent clashes . At least 29 people were treated for cuts , broken bones and birdshot injuries , Health Ministry spokesman Khaled El Khatib said . Six police officers were also hurt in the disorder near Tahrir Square , the Interior Ministry said . What 's behind the latest wave of violence in Egypt ?
Operation Anti-Sexual Harassment/Assault said there were 19 assaults on January 25 . It said its members were often attacked when they intervened . Friday protest marked two-year anniversary of beginning of revolution .