CAIRO -- Egypt's fragile political condition sank toward critical Monday after the military opened fire and killed dozens of Islamists who were demanding the return to office of deposed President Mohammed Morsi. It was the worst political violence in the country since the demonstrations 21/2 years ago that led to the resignation of Hosni Mubarak.
Adly Mansour, the Constitutional Supreme Court judge whom the military named president last week to replace Mr. Morsi, tried to defuse tension by announcing that a new constitution would be submitted to the people for approval within four months, and that elections to select a new Parliament would occur by February. A presidential vote would follow a week after Parliament convened.
But the promise of a quick return to elected leadership seemed unlikely to assuage the bitterness of Morsi supporters targeted by gunfire before dawn outside the Republican Guard headquarters in eastern Cairo, killing an estimated 51.
The Brotherhood's Freedom and Justice political party summoned its supporters to demonstrate today, and Brotherhood members vowed to avenge the deaths, a portent of what is likely to be protracted conflict between the millions who backed the military's removal of Mr. Morsi and those who consider it an illegal coup that removed a democratically elected leader. The Brotherhood said it wouldn't stop its demonstrations or consider reconciliation until Mr. Morsi was back in office.
The military, meanwhile, defended its use of live gunfire, claiming that hundreds of Morsi supporters had opened fire first as they tried to force their way into the Republican Guard facilities, where many think Mr. Morsi is being held. It said two police officers and a soldier died in the attack. At least 435 people were injured.
The top Sunni Islamic cleric warned of potential civil war. Sheikh Ahmed el-Tayeb, leader of Cairo's al-Azhar mosque, issued yet another call for peace, but couldn't hide his frustration. He announced that he would go into seclusion until the crisis ended.
Before Monday's clashes, most of the violence since Mr. Morsi was removed from office Wednesday had been between partisans of the two sides, with 40 killed and 1,000 injured.
But on Monday, for the first time, Egypt's revered military had opened fire on its citizens and caused many casualties, and many feared that there would be no preventing further bloodshed. The Nour Party, the only Islamist body represented in the transitional government, resigned from the government in protest.
Reaction in the streets of Cairo demonstrated the high emotions that have characterized the conflict.
"Kill them all. Why can't they accept that we don't want them!" screamed a fruit vendor named Mohammed, referring to Morsi supporters as he watched television news accounts of what happened.
The scene of the shootings was horrific. Blood ran through the street, which was littered with signs of panic: eyeglasses, shoes and clothing discarded in the rush to find safety. The area smelled of blood.
The dead overwhelmed morgues, and hospitals were hard-pressed to deal with hundreds of wounded.
The army and the Muslim Brotherhood offered different versions of events, and each sought to prove it wasn't responsible for the violence. The military released aerial shots of civilians launching rocks and gunfire at soldiers. The screen's upper-left corner showed three times for the videos -- 4 a.m., 5:55 a.m. and 6:24 a.m. The Brotherhood released videos of their injured being treated in overcrowded hospitals. While the sets of videos showed each side attacking the other, neither definitively showed how the attacks started.
At a news conference, military spokesman Ahmed Mohammed Ali said protesters started the battle, attacking the Republican Guard building and troops stationed there, firing live ammunition. "Any law in the world allows soldiers to defend Egyptian security when confronted with live fire," he said.
Morsi supporters, who have been conducting a sit-in the eastern Cairo district of Rabaa since June 28, a few hundred yards from the Republican Guard building, said soldiers began attacking them in an effort to clear the area as they were praying. Witnesses said the fighting began with tear gas, followed by gunfire.
Ahmed Abdullah, 40, was among those injured, struck with rubber bullets in the leg. Standing outside the mosque, Mr. Abdullah said he had tried to go to the hospital, but an ambulance worker warned him: "If I take you, the police will arrest you." Mr. Abdullah, an oil worker, said, "The officer was laughing while shooting at me and others, as if he were hunting for birds."
State television displayed videos zeroing in on attackers shooting at the army and wounded soldiers being carried away. The military said in a statement that "terrorist groups" had tried to storm the Republican Guard headquarters, and military personnel had protected the entrance. The military said it had arrested 200 protesters, and that dozens of its soldiers were wounded, six critically.
Doctors treating the wounded at the Medical Insurance clinic in Nasr City, a government-run facility, called it "a massacre." Most patients had been wounded in the head, neck and chest, doctors said.