Last Updated 6:45 p.m. ET
CAIRO Officials say 30 people have been killed and more than 200 wounded in clashes around the country involving opponents and backers of ousted President Mohammed Morsi, as well as security forces.
Emergency services official Amr Salama says 12 people died when hundreds of Islamists descended on a rally by opponents of ousted President Mohammed Morsi in the Mediterranean coastal city of Alexandria, opening fire with guns. He says clashes erupted, and police joined on the side of the Morsi opponents.
Meanwhile, an Interior Ministry spokesman says the deputy head of the Muslim Brotherhood, Khairat el-Shater, considered the most powerful man in the organization has been arrested.
Spokesman Hani Abdel-Latif says el-Shater and his brother were arrested late Friday from an apartment in eastern Cairo on allegations of inciting violence against protesters in recent days.
Khaled el-Khatib, a Health Ministry official, says four people were killed near the Republican Guard building in Cairo, where troops opened fire on Morsi supporters marching on the building Friday afternoon.
In Cairo, another person was killed in clashes that erupted after nightfall when Islamists attacked Morsi opponents near Tahrir Square.
Four others died in the northern Sinai city of el-Arish, where Islamists stormed the main government building. Another was killed in the southern city of Assiut.
El-Khatib says 210 people nationwide have been wounded.
Meanwhile, Egyptian military armored vehicles have raced onto a main bridge over the Nile River in Cairo in the first major move to break up the clashes. Several armored vehicles, at least one with young Morsi opponents sitting on the roof, deployed on the 6th of October Bridge, near Tahrir Square, aiming to chase away Morsi supporters. Military helicopters flew toward Tahrir.
The army shooting in Cairo came when hundreds of protesters marched on the Republican Guard building, where Morsi was staying at the time of his ouster Wednesday night before being taken into military custody at an unknown location. The crowd approached a barbed wire barrier where troops were standing guard around the building.
When one person hung a sign of Morsi on the barrier, the troops tore it down and told the crowd to stay back. A protester put up a second sign, and the soldiers opened fire, according to an Associated Press photographer.
Many of those injured had the pockmark wounds typical of birdshot. The BBC's Middle East editor, Jeremy Bowen, was hit by birdshot in the head as he covered the clashes. "Am fine," he reported in a Tweet.
Protesters pelted the line of troops with stones, and the soldiers responded with volleys of tear gas.
The clashes appeared to ease with the start of midafternoon prayers.
Britain's Foreign Secretary William Hague said he was "very concerned" by the reports of violence. In a Twitter message, he wrote: "Hope calm heads will prevail, vital to avoid escalation."
The top leader of Egypt's Muslim Brotherhood, General Guide Mohammed Badie, who was taken into custody by security forces soon after the military ousted Morsi, was released from detention Friday.
Badie later delivered a speech at a rally in support of the ousted president, vowing to "gain our rights."
He led the crowd of tens of thousands in a chant: "Free revolutionaries, we will continue the path."