CAIRO -- Security forces and armed civilian men clashed with supporters of Egypt's ousted president early Saturday, killing at least 65 protesters in mayhem that underscored an increasingly heavy hand against demonstrations demanding Mohammed Morsi's return to office.
In chaotic scenes, pools of blood stained the floor and bodies were lined up under white sheets in a makeshift hospital near the site of the battles in eastern Cairo. Doctors struggled to cope with the flood of dozens of wounded, many with gunshots to the head or chest.
It was the deadliest single outbreak of violence since the military ousted the Muslim Brotherhood-backed Morsi on July 3 and one of the deadliest in 2 1/2 years of turmoil in Egypt.
The extent of the bloodshed pointed to a rapidly building confrontation between the country's two camps, sharply divided over the coup that removed Egypt's first freely elected president after widespread protests against his Islamist rule.
Authorities talk more boldly of making a move to end weeks of protests by Morsi's largely Islamist supporters. At the same time, the Islamists are growing more assertive in challenging security forces as they try to win public backing for their cause.
Saturday's clashes were sparked when pro-Morsi protesters sought to expand their main Cairo sit-in camp by moving onto a main boulevard, only to be confronted by police and armed civilians -- reportedly residents of nearby neighborhoods. Police initially fired tear gas but, in ensuing clashes, the protesters came under gunfire.
Officials from the Muslim Brotherhood and their allies decried what they called a new "massacre" against their side, only weeks after July 8 clashes with army troops in Cairo that left more than 50 Morsi supporters dead.
Secretary of State John Kerry said that he spoke to Egyptian authorities, saying it is "essential" they respect the right to peacefully protest. He called on all sides to enter a "meaningful political dialogue" to "help their country take a step back from the brink."
However, neither side has shown much taste for reconciliation. Islamists staunchly reject the new leadership and insist that the only possible solution to the crisis is to put Morsi back in office. Meanwhile, the interim leadership is pushing ahead with a fast-track transition plan to return to a democratically elected government by early next year.
Also, the military-backed authorities appear confident of public support for a tougher hand after millions turned out for nationwide rallies Friday called by army chief Gen. Abdel-Fattah el-Sissi as a mandate against "terrorism and violence."
Interior Minister Mohammed Ibrahim, who is in charge of police, took an uncompromising stance at a news conference after the violence. He accused the pro-Morsi side of provoking bloodshed to win sympathy.
"We didn't go to them; they came to us -- so they could use what happened for political gain," he said.
Ironically, Ibrahim was a Morsi appointee, and his then-boss praised him for a tough hand after police killed dozens of anti-Morsi protesters in the city of Port Said earlier this year.
"The Ministry of Interior never has and never will fire on any Egyptian," he said, saying police only fired tear gas in Saturday's violence.
He suggested authorities could take the more explosive step of moving against the two main pro-Morsi protest camps in Cairo: weeks-old sit-ins, on outside the Rabaah al-Adawiya in eastern Cairo and another in Nahda Square in Cairo's sister city of Giza.
He depicted the encampments as a danger to the public, citing 10 bodies police that have been found nearby in recent days. Some had been tortured to death, police have said, apparently by members of the sit-ins who believed they were spies.
"Soon," Ibrahim said, "we will deal with both sit-ins."
Interim Vice President Mohamed ElBaradei, a longtime pro-democracy campaigner who backed the military's ouster of Morsi, raised one of the few notes of criticism of Saturday's bloodshed.