Clashes also erupted at Monday's funeral of another activist, Mohammed al-Guindi, 28, who was arrested last month after joining protests demanding change on the second anniversary of the country's uprising.

Egypt's opposition says Guindi's death proves the police have not reformed since the uprising to topple authoritarian leader Hosni Mubarak.

State Department spokeswoman Victoria Nuland said the US was was "extremely disturbed by these incidents, including sexual assaults against women and the beating of a defenseless man last week."

"We urge the government of Egypt to thoroughly, credibly and independently investigate all claims of violence and wrongdoing by security officials and demonstrators and to bring perpetrators to justice. Accountability is the best way to prevent recurrences of these kinds of incidents."

Egyptian policemen were filmed beating and dragging a naked man during protests in Tahrir Square on Friday, prompting Culture Minister Mohammed Saber Arab to resign, Egyptian state media reported.

Egypt's presidency said meanwhile in a Facebook statement that it had asked the public prosecutor to probe Guindi's death, stressing there is "no return to rights abuses of citizens and their freedoms... after the January 25 revolution."

Nuland agreed, urging Morsi "to be the president for all Egyptians."

"All Egyptians, regardless of gender, political affiliation or religion, deserve the right to safely assemble in public without fear of violence. And we call on the Egyptian government to make that possible," she added.