Protests by supporters of ousted Islamist President Mohamed Morsi turned violent across Egypt on Friday, with witnesses and security reporting at least 72 dead across the country as the Muslim Brotherhood staged a "Day of Rage".
The army deployed dozens of armored vehicles on major roads around the capital after Morsi's Brotherhood movement called the demonstrations, and the Interior Ministry said police would use live ammunition against anyone threatening public buildings.
The violence followed Wednesday's assault by security forces on two Brotherhood sit-ins in Cairo that left hundreds dead, as security forces tried to end weeks of turbulence following the army's toppling of Morsi on July 3.
In Cairo gunshots echoed around the huge Ramses Square, focal point of Brotherhood protests in the capital, and police fired salvos of tear gas. At least 50 people were killed and many more wounded by gunshot and birdshot in the square, security officials said.
Nile TV showed footage of one gunman among Islamist protesters firing from a city center bridge. Injured men, one with a bloody wound in the middle of his chest, were rushed away on the back of a pick-up truck.
Emergency services also said eight protesters were killed in clashes in the Mediterranean town of Damietta, and four people died in the northeastern city of Ismailia. A local hospital official said five people were killed in Fayoum, and 70 were injured.
Violence was also reported in Egypt's second city Alexandria, while five were killed and 15 others injured, and in the Nile Delta city of Tanta.
Scuffles broke out in Cairo and a police conscript was killed in a drive-by shooting in the north of the capital, state news agency MENA reported.
Tear gas was fired and shooting was heard on Friday at the main Cairo square where protests ensued, a Reuters witness said.
Two witnesses said they saw protesters throw petrol bombs at a police station near the square.
Deeply polarized Egypt has been bracing for further confrontation expected after Friday prayers between members of Morsi's Muslim Brotherhood and the army-backed government.
The Brotherhood called for a nationwide march of millions to show anger at the ferocious security crackdown on Islamists.
They have demanded the resignation of army commander General Abdel Fattah al-Sisi and the reinstatement of Egypt's first freely elected president, who is in detention and has not been seen in public since his downfall.
"Sooner or later I will die. Better to die for my rights than in my bed. Guns don't scare us anymore," said Sara Ahmed, 28, a business manager, joining a march of thousands of demonstrators heading downtown from northeast Cairo.
"It's not about the Brotherhood, it's about human rights," said Ahmed, one of the few women not wearing a headscarf, a sign of piety for Muslim women.
When a military helicopter flew low over Ramses Square, protesters held up shoes chanting "We will bring Sisi to the ground" and "Leave, leave, you traitor."
As the sound of teargas canisters being fired began, protesters - including young and old, men and women - donned surgical masks, gas masks and wrapped bandannas around their faces. Some rubbed Pepsi on their faces to counter the gas.
"Allahu akbar! (God is Greatest)" the crowd chanted.
After protesters torched a government building in Cairo on Thursday, the authorities said security forces would turn their guns on anyone who attacked the police or public institutions.
Wednesday's bloodshed was the third mass killing of Morsi's supporters since his ouster. The assault left his Muslim Brotherhood in disarray, but it said it would not retreat in its showdown with army commander General Abdel Fattah al-Sisi.
"After the blows and arrests and killings that we are facing, emotions are too high to be guided by anyone," said Brotherhood spokesman Gehad El-Haddad.

"Pain and sorrow"

A Brotherhood statement called for a nationwide "march of anger" by millions of supporters on Friday after noon prayers.
"Despite the pain and sorrow over the loss of our martyrs, the latest coup makers' crime has increased our determination to end them," it said.
The Brotherhood accuses the military of staging a coup when it ousted Morsi. Liberal and youth activists who backed the military saw the move as a positive response to public demands.
But some fear Egypt is turning back into the kind of police state that kept Mubarak in power for 30 years, as security institutions recover their confidence and reassert control.
Friday prayers have proved a fertile time for protests during more than two years of unrest across the Arab world.
In calling for a "Friday of anger," the Brotherhood used the same name as that given to the most violent day of the uprising against former President Hosni Mubarak. That day, January 28, 2011, marked the protesters' victory over the police, who were forced to retreat while the army was asked to intervene.
In a counter-move, a loose liberal and leftist coalition, the National Salvation Front, called on Egyptians to protest on Friday against the Brotherhood's "obvious terrorism actions".
Signalling his displeasure at the worst bloodshed in Egypt for generations, US President Barack Obama said on Thursday normal cooperation with Cairo could not continue and announced the cancellation of military exercises with Egypt next month.
"We deplore violence against civilians. We support universal rights essential to human dignity, including the right to peaceful protest," he said, but stopped short of cutting off the $1.55 billion a year of mostly military US aid to Egypt.
The United States on Thursday told its citizens to leave Egypt due to the unrest. It issued the same advice last month.
The Egyptian presidency issued a statement saying Obama's remarks were not based on "facts" and would strengthen and encourage violent groups that were committing "terrorist acts".
Pro-army groups posted videos on the Internet of policemen they said had been tortured and killed by Islamist militants.
Washington's influence over Cairo has been called into question since Morsi's overthrow. Since then Saudi Arabia, Kuwait and the United Arab Emirates have pledged $12 billion in assistance, making them more prominent partners.
Obama's refusal so far to cut off US aid to Egypt suggests he does not wish to alienate the generals despite the scale of the bloodshed in the army's suppression of Morsi supporters.
Egypt will need all the financial support it can get in the coming months as it grapples with growing economic woes, especially in the important tourism sector that accounts for more than 10 percent of gross domestic product.
The United States urged its citizens to leave Egypt on Thursday and two of Europe's biggest tour operators, Germany's TUI and Thomas Cook Germany, said they were cancelling all trips to the country until Sept. 15.
On Thursday, the UN Security Council urged all parties in Egypt to exercise restraint, but did not assign blame.
"The view of council members is that it is important to end violence in Egypt," Argentine UN Ambassador Maria Cristina Perceval said after the 15-member council met on the situation.