Updated 10:59 PM ET
CAIRO Called out by the army, the largest crowds in 2 1/2 years of upheaval filled Egypt's streets Friday, while ousted President Mohammed Morsi was formally placed under investigation on a host of allegations including murder and conspiracy with the Palestinian militant group Hamas.
Morsi's supporters also showed no signs of backing down, though they turned out in vastly smaller numbers. The demonstrations in Cairo were mostly peaceful into the evening. But by late Friday night in Cairo, police fired tear gas to disperse hundreds of Morsi supporters near a sit-in they held for weeks, setting off clashes that lasted into early Saturday morning in a possible sign of a new intolerance for marches that block city streets. A field hospital doctor said seven protesters were killed and hundreds injured.
In the city of Alexandria, seven people were killed and over 100 were injured in clashes between supporters and opponents of Morsi, officials said.
The announcement by prosecutors of the investigation against Morsi, which is likely to pave the way to a formal indictment and eventually a trial, was the first word on his legal status since he was deposed by the military July 3. Since then, the Islamist leader has been held incommunicado in a secret location.
Both sides tried to show how much public support they enjoy. But the millions who turned out for the pro-army demonstrations overwhelmed the streets in multiple cities in Egypt, including some that rarely seen any rallies since the 2011 uprising.
Throngs of people turned out in Cairo's Tahrir Square and in other cities, answering a call by army chief Gen. Abdel-Fattah el-Sissi, who urged them to give him a mandate to stop "potential terrorism" by supporters of Morsi's Muslim Brotherhood.
Portraits of the smiling el-Sissi in sunglasses dominated the crowd in Tahrir and one near the presidential palace across town. Posters with his picture were emblazoned with the words "the love of the people," and demonstrators wore small photos of him around their necks or carried a picture of his face on an Egyptian one-pound note.
Security was heavy after el-Sissi vowed to protect the rallies from attacks by rivals. Tanks guarded one entrance to Tahrir and police were stationed at other parts.
"The army is here to protect the people. They don't lie," said Ezzat Fahmi, a 38-year-old in the crowd. He said el-Sissi called the rallies "so the entire world can see that the Egyptian people don't want the Brotherhood anymore."
El-Sissi's plea came at a time when the political standoff with Morsi's supporters showed no sign of resolution. Reporting from Cairo's Tahrir Square,that el-Sissi's call for rallies was being interpreted by many as the beginning of a major crackdown on the Muslim Brotherhood.
Meanwhile, the allies of the toppled president have held a sit-in outside the Rabaa al-Adawiyah Mosque in Cairo and near daily rallies elsewhere in the capital for three weeks.
The rallies have often turned violent, with more than 180 people killed this month. The Morsi supporters and opponents blame each other for the bloodshed, and people in both camps have been seen carrying weapons.
The unrest, as well as claims that Islamist groups are stockpiling weapons and escalating attacks against troops in the Sinai, were used by the country's new military-backed rulers as a basis for demanding popular support.
The interim leader, Adly Mansour, told the private TV station al-Hayat that his government seeks to include everyone, but it will not accept lawlessness, blocked roads and attacks on state institutions. He urged the pro-Morsi protesters to go home, promising they won't be pursued or arrested.
"I can't negotiate with whoever has committed a crime. But those who were duped or those who want to belong to Egyptian society, we welcome them," he said. But he added: "The state must interfere (against lawlessness) firmly."
Not long after the speech, police moved in quickly to break up a crowd of Morsi supporters marching on a main overpass in Cairo near the pro-Morsi sit-in, firing tear gas. Clashes with security forces ensued as protesters tried to extend their sit-in beyond the mosque into a main boulevard. Mahmoud Zaqzouq, a Brotherhood official, said a number of protesters had minor wounds.
Interior Minister Mohammed Ibrahim told a private TV station that the sit-in at the Rabaa mosque will be removed by legal means. He did not elaborate but said residents of the area have filed police reports against the encampment.
Police spokesman Hani Abdel-Latif told The Associated Press that 53 pro-Morsi supporters were arrested around Egypt on Friday in possession of weapons, ranging from knives to homemade guns.
El-Sissi deposed Morsi after four days of huge protests by millions of Egyptians demanding the removal of the country's first freely elected president following months of disagreements between him and the largely secular opposition.
The accusations against Morsi are connected to a prison break during the 2011 uprising against autocrat Hosni Mubarak. Gunmen attacked the Wadi el-Natroun prison northwest of Cairo, freeing inmates, including Morsi and about 30 other figures from the Muslim Brotherhood. The prosecutors allege Morsi and the Brotherhood worked with Hamas to carry out the break, in which 14 guards were killed.
Egypt's MENA news agency said Morsi was being investigated over allegations of collaborating with Hamas "to carry out anti-state acts, attacking police stations and army officers and storming prisons, setting fire to one prison and enabling inmates to flee, including himself, as well as premeditated killing of officers, soldiers and prisoners."