Angry Egyptians emerged from midday prayers and took to the streets in a show of defiance, igniting a series of deadly clashes that quickly spread across the country.
Health officials say at least 70 people were killed in Friday's fighting, most of them in violence in and around Cairo's Ramses Square. Some news reports put the death toll much higher, while witnesses say they saw dozens of bodies laid out in mosques that have become makeshift morgues.
The renewed violence gripped Egypt as supporters of ousted president Mohamed Morsi and his Muslim Brotherhood defied a state-of-emergency to hold a "Day of Rage."
The protests quickly descended into chaos. Video shows residents pelting Muslim Brotherhood supporters with rocks as well as plain-clothed Egyptians firing at each other in running street battles. The Muslim Brotherhood said a military aircraft opened fire on demonstrators.
Near Ramses Square, fire engulfed the building that houses a construction company. It was not clear how the fire started.
Clashes were also reported between protesters and security forces in Alexandria, Fayoum, Suez, Ismailia, Tanta and El Arish. Despite a night time curfew many protesters remained on the streets into the night.
The office of Egypt's interim president said he would hold a news conference on Saturday to talk about the latest developments.
The confrontations follow Wednesday's government crackdown on two pro-Morsi camps in Cairo. The government says 638 people were killed during the crackdown, but the Muslim Brotherhood says the death toll is in the thousands.
Earlier Friday, Egyptian state media warned people to stay off the streets in Cairo as an operation to confront what it calls "terrorist elements" unfolds. Officials had previously warned that security forces would use live ammunition if any government facilities were attacked.
In a Skype interview from Cairo, VOA correspondent Elizabeth Arrott described how protesters in Cairo reacted as they heard shots fired.
"All of a sudden there will be a noise and the entire crowd in unison will duck down, which is an indication that there are some kinds of shots being fired. It is not clear exactly what kind. Not tear gas or we would have seen the plumes of smoke."
At the U.N., Egyptian Ambassador Mootaz Ahmadein Khalil told reporters his government is willing to work with all factions of society.
"We will have a political inclusive, an inclusive political process that will include all members of Egyptian society no matter what they think as long as they do not resort to violence."
Meanwhile, the U.N. announced it was sending its political affairs chief Jeffrey Feltman to Egypt next week for consultations with Egyptian authorities.
French President Francois Hollande and German Chancellor Angela Merkel have called for European Union foreign ministers to meet next week to discuss Egypt's crisis. In a Friday statement, they also called for an immediate end to the unrest.
U.S. President Barack Obama has canceled next month's scheduled military exercises with Egypt. He says traditional cooperation cannot continue when civilians are being killed in the streets.
On Friday, two U.S. Republicans senators called on Mr. Obama to suspend all aid to Egypt.
Senators John McCain and Lindsey Graham traveled to Egypt last week at the behest of Mr. Obama. In their statement, they said Egypt's interim government and the military are, "taking Egypt down a dark path, one that the United States cannot and should not travel with them.''
The U.S. provides Egypt with $1.3 billion in military aid each year.