CAIRO - Hundreds of thousands of Egyptians took to the streets in rival mass rallies on Friday, hours after the state news agency said ousted Islamist president Mohamed Mursi was being investigated for charges including murder.
In Cairo, huge crowds heeded a call by army chief General Abdel Fattah al-Sisi to give him a popular mandate to confront violence unleashed by his July 3 overthrow of Mursi, many of them clutching pictures of the general in full ceremonial uniform.
Supporters of the deposed Islamist leader staged mass counter-demonstrations to demand his reinstatement, shrugging off fears of an imminent crackdown.
The army's move against Egypt's first democratically elected president has caused deep alarm in the West.
The country of 84 million people forms a bridge between the Middle East and North Africa and receives US$1.5 billion (S$1.9 billion) a year in mainly military aid from the United States (US).
Highlighting the potential for bloodshed, hospital officials said four people were killed in clashes in Egypt's second city Alexandria - three stabbed and one shot in the head. More than 50 were wounded.
A Reuters reporter said hundreds of people fought a pitched battle in the city, with birdshot fired and men on rooftops hurling stones down at the crowds below.
Seven protesters were also reported hurt in the Nile delta city of Damietta.
The capital was largely peaceful, but numbers were expected to peak in the evening, when clashes have broken out before.
Close to 200 people have died in violence in the three weeks since the army deposed the president.
The army has made clear it sees Friday as a turning point in its confrontation with Mursi's Muslim Brotherhood, which emerged from decades in the shadows to win successive elections after Egypt's 2011 Arab Spring uprising against veteran autocrat Hosni Mubarak.
It lasted a year in government, during which the economy floundered and Mursi's popularity slumped.
"The Brothers stole our revolution," said Mr Salah Saleh, a horse trainer at a central Cairo rally, voicing widespread criticism that Mursi refused to share out power after taking office, and then failed to tackle Egypt's many woes.
"They came and sat on the throne and controlled everything."
Many thousands of men, women and children joined Brotherhood supporters at their round-the-clock vigil in north-east Cairo, which is close to army installations but far from Tahrir Square, focal point for the pro-army rally.
"It is either victory over the coup or martyrdom," said senior Brotherhood politician Mohamed El-Beltagy told the pro-Mursi rally. "Our blood and our souls for Islam!" the crowds chanted.
The military had warned it would "turn its guns" on those who used violence. The Brotherhood, which has manned a month-long tent vigil in Cairo, warned of civil war.
It accuses the army and hired thugs of stoking trouble to justify a move against the Islamists.
In Cairo, helicopters repeatedly buzzed low over the pro-Mursi vigil before wheeling around Tahrir Square, and scattering Egyptian flags over the packed supporters.
"The Muslim Brotherhood has deviated from the path of real Islam," said Mr Gamal Khalil, a 47-year-old taxi driver as his wife and two daughters waved flags at passing cars on a bridge over the Nile.
"The army is the only honest institution in the country," he said. "They're keeping my whole family safe."
The probe against Mursi centres on charges he conspired with Palestinian Islamist group Hamas to flee jail during the 2011 uprising against Mubarak, killing some prisoners and officers, kidnapping soldiers and torching buildings.
Mursi has previously said locals helped him escape from prison during the upheavals, and the Muslim Brotherhood denounced the series of accusations levelled against him. Hamas challenged investigators to find "one piece of evidence" that it had meddled in Egyptian affairs.
"At the end of the day, we know all of these charges are nothing more than the fantasy of a few army generals and a military dictatorship," Brotherhood spokesman Gehad El-Haddad said. "We are continuing our protests on the streets."
State news agency Mena said Mursi had been ordered detained for 15 days pending the probe.
Convulsed by political and economic turmoil, Egypt is deeply polarised, struggling to make the transition from the autocratic rule of the discredited Mubarak to free and open democracy.
Signalling its displeasure at recent events, Washington said this week it had delayed delivery of four F-16 fighter jets to Cairo and called on the Egyptian army to exercise "maximum restraint and caution" during Friday's rallies.
One security source said the military wanted to calm the situation after realising that Sisi's call to rally was not well received abroad. A military statement on Facebook said the protests did not represent a threat to the Brotherhood.
State television screened images on Friday of the celebrations that erupted the night Sisi announced Mursi had been deposed. The narrator declared it "the day of liberation from the Brotherhood occupation".
"Egypt against terrorism," declared a slogan on the screen.
Army chief Sisi delivered his call for rallies on Wednesday in full military uniform and dark sunglasses. He was appointed by Mursi in a bid by the president to rein in Egypt's powerful military, but Mr Sisi turned against him.
He has appointed an interim government tasked with preparing for new parliamentary elections in about six months to be followed by a new presidential ballot. The Brotherhood says it will not join the process.