WASHINGTON/UNITED NATIONS - US Secretary of State John Kerry has urged Egypt's leaders to pull the restive nation "back from the brink" as Saturday's violence left scores dead and injured.

At UN Headquarters in New York, UN Secretary-General Ban Ki-moon strongly condemned the deadly upsurge of violence and called on Egyptian security forces to respect the right to free speech

and assembly while urging protesters to demonstrate peacefully. The Egyptian Health Ministry said 72 people had been killed in the clashes between supporters of ousted President Mohamed Morsi and the interim government's security forces, The New York Times reported.

Morsi's party, the Muslim Brotherhood, said it had counted 66 dead with 61 others "clinically dead," the newspaper said.

By the Brotherhood's count, 4,500 were injured, while the Health Ministry said only 177 were hurt, Ahram Online reported earlier. Kerry said he spoke with interim Vice President Mohamed ElBaradei, interim Foreign Minister Nabil Fahmy and European Union High  Representative Catherine Ashton, expressing the Obama administration's "deep concern about the bloodshed and violence in Cairo and Alexandria" he said had "claimed the lives of scores of Egyptian demonstrators and injured more than 1,000 people." Kerry called the situation "a pivotal moment for Egypt."

"In this extremely volatile environment, Egyptian authorities have a moral and legal obligation to respect the right of peaceful assembly and freedom of expression," Kerry said. "Both are essential components of the inclusive democratic process they have publicly embraced.

"Violence not only further sets back the process of reconciliation and democratization in Egypt, but it will negatively impact regional stability. "At this critical juncture, it is essential that the security forces and the interim government respect the right of peaceful protest, including the ongoing sit-in demonstrations."

Kerry said the United States urges an independent and impartial investigation into the latest violence and called on "leaders across the olitical spectrum to act immediately to help their country take a step back from the brink."

The violent confrontations occurred in Nasr City, a stronghold of Morsi and the Muslim Brotherhood. Interior Minister Mohammed Ibrahim early Saturday vowed to end a sit-in by Morsi supporters at the Raaba al-Adawiya mosque, saying it would be "brought to an end soon and in a legal manner," the BBC reported. A Brotherhood supporter who gave his name as Karim told Ahram Online police had used both tear gas and live fire in Nasr City. Police have denied using live fire on protesters.

The National Alliance to Support Legitimacy, a pro-Morsi coalition, issued a statement calling the deaths of protesters a "massacre."

Dr Omar Amer, working at an improvised field hospital, told al-Jazeera the hospital had run out of supplies and medical workers.