CAIRO -- Egypt's bitter split over who should be ruling the country exploded into violent clashes in the streets of Cairo and elsewhere Friday, as masses of demonstrators celebrating the ouster of President Mohammed Morsi battled crowds of Islamists who wanted him reinstated.
Combatants used rocks, sticks, fireworks and gasoline bombs in a battle lasting hours that raged near Tahrir Square and across a bridge spanning the Nile River, part of the most widespread street violence in Egypt since the early days of the 2011 revolution.
The mayhem capped a day full of massive and defiant protests by Islamists demanding Mr. Morsi be returned to power. At least four people were killed, and many wounded, when security forces fired into a protest near the officers' club of the powerful Republican Guard, where many believed Mr. Morsi was detained.
With clashes breaking out late into the night, it was impossible to estimate the full extent of casualties and damage. But early today, security officials said at least 30 people had been killed nationwide and hundreds wounded, many of them in Cairo.
Islamists in other cities also demanded Mr. Morsi's reinstatement, breaking into government offices in several provinces and temporarily evicting military officials. Fifteen people died in Alexandria alone, and a curfew was declared in the Sinai Peninsula, where six soldiers and police officers were killed in at least four attacks on security posts.
The new violence suggested that the military's removal of Mr. Morsi, the country's first freely elected president, following protests by millions of Egyptians angry with his rule, had worsened the deep polarization between Islamists who call his ouster a military coup and their opponents, who say his removal was the result of an urgent need to fix Egypt's myriad problems.
By turning out in the tens of thousands, pro-Morsi crowds underlined the organizational might of the Muslim Brotherhood, which emerged as the major political force and dominated rounds of elections after Egypt's revolution two years ago. At that time, it gained power that many in the group had dreamed of for decades. The military's intervention in politics this week entirely removed it from the government.
The group called the protests the "Friday of Rejection" and chanted for Mr. Morsi's return.
"We will bring him back, bearing him on our necks, sacrifice our souls for him," Mohammed Badie, the group's spiritual leader, told enraged crowds at a large demonstration in the Cairo suburb of Nasr City. "We will bring back the rights of the Egyptian people, who were wronged by this disgraceful conspiracy."
Mr. Badie said reports were false that he was among Islamist leaders arrested in a post-Morsi crackdown by security forces. Hundreds of Islamists were detained within a day after Mr. Morsi's ouster. Some were released Friday.
An interim president installed by the military, Adli Mansour, a former chief justice of the Supreme Constitutional Court, took a further step Friday to erase vestiges of Mr. Morsi's government by formally dissolving the Shura Council, Egypt's only operating house of Parliament, which the Islamists had dominated. The constitutional court had disbanded the lower house last year, one of many challenges that Mr. Morsi had faced in his troubled tenure.
In a further affront to Islamists, the Egyptian news media have marginalized their message in the two days since Mr. Morsi was deposed. Despite the interim government's pledge of inclusiveness, Islamist television broadcasters were shuttered, and state television barely covered the breadth of the pro-Morsi demonstrations Friday.
Underpinning the Islamists' fears of the emerging political order was a keen awareness of the long history of enmity with the security services. While some Islamists did use violence against the state, Egypt's previous rulers kept their power in check by banning their organizations and subjecting members to arbitrary arrests and torture. For some, those memories have come flooding back.
"They hung me up, they beat me, they used electricity -- all the means of torture they had," said Hussein Nada, 43, a protester, recalling eight years he spent in prison for his association with the Gamaa al-Islamiyya, a radical Islamist group that attacked tourists and other targets in the 1990s but has renounced violence in recent years.
"Anyone from the opposition who came to power could decide to put us all back in prison," he said. "As soon as the army came back, they put hundreds on the arrests list, so we fear we could lose all we've gained."
The shooting outside the Republican Guard officers' club broke out after protesters had reacted angrily to an officer who shredded a Morsi poster that had been hung on barbed wire blocking the entrance. Blood stained the sidewalk where the wounded had fallen, and the protest crowd soon swelled, as angry Islamists from elsewhere joined in.
"Where's Morsi?" they screamed. Others denounced Egypt's defense minister, Gen. Abdel-Fattah el-Sissi, who ordered Mr. Morsi's removal Wednesday. "Traitor, traitor, traitor! Sissi is a traitor!" they cried.
The clashes downtown erupted when masses of Morsi supporters marched across a bridge spanning the Nile to try to enter Tahrir Square, epicenter of the uprising that toppled President Hosni Mubarak, which has been the main spot for aggrieved Egyptians ever since. Anti-Morsi demonstrators camped in the square rushed to keep them out, and the two sides clashed on and around a bridge near the Ramses Hilton Hotel and the Egyptian Museum.
Military helicopters circled as the two sides faced off, each protecting its front line with huge sheets of metal. Rioters pelted each other with rocks and chunks of concrete and lobbed fireworks over their opponents' heads, showering them with a rain of red, green and blue sparks.
Pro-Morsi rioters surged onto the bridge, and a battle raged over the Nile for hours until dozens of armored vehicles packed with black-clad riot police were deployed.