* Violence reported in several places after Friday prayers
* Armoured army vehicles deployed across Cairo
* Muslim Brotherhood says not ready to retreat in battle
By Tom Perry and Yasmine Saleh
CAIRO, Aug 16 (Reuters) - Thousands of supporters of ousted President Mohamed Mursi took to the streets on Friday, urging a "Day of Rage" to denounce this week's assault by security forces on Muslim Brotherhood protesters that killed hundreds.
The army deployed dozens of armoured vehicles on major roads in Cairo, and the Interior Ministry has said police will use live ammunition against anyone threatening state installations.
Medical sources said four protesters died in clashes in the northeastern city of Ismailia, with one dead reported in the Mediterranean port of Damietta.
Violence was also reported in Egypt's second city Alexandria 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.
Deeply polarised after months of political turmoil, Egypt stands on the abyss of nationwide chaos with Islamist supporters refusing to accept the July 3 toppling of Mursi following mammoth rallies castigating his trouble-plagued, year-long rule.
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.
Looking to end the crisis, police on Wednesday cleared out two protest camps in Cairo set up by the Muslim Brotherhood. The Health Ministry said at least 578 died in the onslaught, but the Brotherhood says thousands were killed.
"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.
Thousands of Mursi supporters were also gathered in Ramses Square in central Cairo. When a military helicopter flew low over the area, protesters held up shoes chanting "We will bring Sisi to the ground" and "Leave, leave, you traitor."
Signalling his displeasure at the worst bloodshed in Egypt for generations, U.S. 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 U.S. aid to Egypt.
The Brotherhood accuses the military of staging a coup when it ousted Mursi. 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 the disgraced Hosni Mubarak in power for 30 years before his removal in 2011, 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 "Day of Rage," the Brotherhood used the same name as that given to the most violent day of the uprising against Mubarak. That day, Jan. 28, 2011, marked the protesters' victory over the police, who were forced to retreat.
Underscoring the deep divisions in the most populous Arab state, local residents helped the army block access to Cairo's Rabaa al-Adawiya mosque, the site of the main Muslim Brotherhood sit-in that was swept away on Wednesday.
"We are here to prevent those filthy bastards from coming back," said Mohamed Ali, a 22-year-old business student.
The Egyptian presidency issued a statement criticising Obama, saying his comments were not based on "facts" and would strengthen 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 Mursi'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 U.S. aid to Egypt suggests he does not wish to alienate the generals despite the scale of the bloodshed in the army's suppression of Mursi 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 U.N. 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 U.N. Ambassador Maria Cristina Perceval said after the 15-member council met on the situation.