Coptic Christians make up between six and ten per cent of Egypt's population and their community has been the target of sectarian violence in the past.
Already yesterday several Egyptian churches were burned by mobs of Morsi's Islamist supporters, angered by the deadly police assault on their sit-in demonstrations in Cairo.
In a statement, Adama Dieng, UN Special Adviser on the Prevention of Genocide, and Jennifer Welsh, UN Special Adviser on the Responsibility to Protect, condemned the violence by the security forces.
"We call all political and social actors to abandon strategies of confrontation, engage constructively to ensure respect for diversity, and take all possible steps to facilitate peaceful resolution of disputes in the country," the authors said.
According to an updated government toll at least 525 people were killed -- 482 civilians and 43 police -- and 3,500 injured in yesterday's violence, and deadly clashes were continuing today.