The United Nations secretary general for human rights wants an independent investigation into the killing of protestors in Egypt in recent days.
Navi Pillay says the evidence is that military and security forces inflamed the situation.
At least 35 people have died since the weekend in clashes between police and protesters.
Clashes have again erupted despite confirmation from the military on Wednesday of a faster handover to civilian rule.
A BBC reporter in Cairo's Tahrir Square, where the protests have centred, says the political concessions by the military have done nothing to take the heat out of the fierce confrontation between protesters and police.
The demonstrators are calling for the immediate resignation of the head of the ruling military council.
The director of the United Nations Information Centre in Egypt, Khalwa Mattar, says Cairo is on the brink of chaos.
"The situation is extremely tense and sad at the same time," she says.
"People are worried that this will lead to escalation of the situation instead of calming it down."
Tens of thousands of people are still gathered in Tahrir Square.