Graphic footage, apparently filmed on Sunday during the inauguration of new President Abdel Fattah al-Sisi using a mobile phone, shows a mob of men surrounding the young woman, who was stripped of her clothes and badly bruised in the assault in Cairo's iconic Tahrir Square.

Washington on Tuesday slammed an "horrific" video of a woman being sexually assaulted in Cairo and urged the new government to stand by a vow to stamp out such attacks.

The video "shocked and appalled us as much as it did the Egyptian people," State Department spokeswoman Jen Psaki told reporters.

"We urge the government to make good on its promise to do whatever it takes to combat sexual harassment and implement the new law that punishes convicted harassers," she said.

Graphic footage, apparently filmed on Sunday during the inauguration of new President Abdel Fattah al-Sisi using a mobile phone, shows a mob of men surrounding the young woman, who was stripped of her clothes and badly bruised in the assault in Cairo's iconic Tahrir Square.

"The prevalence of sexual assaults against Egyptian women is a cause of great concern, not just to the Egyptian people but to the United States and the international community," Psaki said.

She also called on the new government to make "serious efforts to end sexual violence in Egypt ... and to ensure that there is no impunity for attacks against women."