By nightfall Friday, state-run media reported sporadic fighting between roving bands of armed protesters and residents in Cairo, where military helicopters could be seen patrolling from the sky as soldiers fanned out across the streets.
Smoke wafted through Ramses Square from a fire that engulfed a nearby commercial building. It was unclear what caused the fire.
Earlier in the day, A CNN crew witnessed men in plainclothes standing next to military tanks and firing into crowds. The crew also saw that some in the crowd were armed.
Security forces fired tear gas at a mass of people on a major bridge leading to the centrally located Ramses Square. Machine-gun fire was heard in central Cairo as a military helicopter flew overhead.
Elsewhere in Cairo, armed groups were reportedly firing from rooftops, attempting to down a military surveillance helicopter, state-run media reported, citing security sources.
Armed protesters also attacked a police station in central Cairo, killing the police chief, state-run EGYNews reported.
Since Wednesday, 52 police officers have been killed, state television reported. Earlier reports of 64 dead were incorrect. State TV also said 25 police stations and 10 churches have been attacked. The interim government has blamed the Muslim Brotherhood for the attacks.
At least 263 people, described by armed members of the Muslim Brotherhood, have been arrested across the country, according to the Egyptian Ministry of Information.
"The struggle to overthrow this illegitimate regime is an obligation," the Muslim Brotherhood said on its website Friday, while urging people to protest peacefully.
Echoes of violence
The violence echoed the upheaval that preceded the popular uprising that ousted Hosni Mubarak from power in 2011. The military removed Mubarak after protests against his authoritarian rule, but not before an estimated 840 people were killed.
The generals yielded power to Morsy after elections, but the new president soon was accused of pursuing an Islamist agenda and excluding other factions from the government. The military ousted Morsy from office on July 3, a move that triggered massive protests among his supporters.
Morsy's supporters say the deposed president wasn't given a fair chance and that the military has returned to its authoritarian practices of the Mubarak era.
The government reinforced the comparison by imposing the month-long state of emergency, a favored tactic of Mubarak.
Morsy and key members of the Muslim Brotherhood have been detained.
The most senior Muslim Brotherhood leader still at large, Essam el-Erian, said Thursday the protests will continue until Morsy is returned to office.
"They can arrest me and 100 of us, but they can't arrest every honorable citizen in Egypt," el-Erian told CNN. "They can't stop this glorious revolution."
Military vehicles were deployed Friday across Cairo and Giza, taking up positions in squares and securing important institutions, EGYNews reported, citing security officials.
The news agency said the military increased checkpoints at all entrances to Cairo to prevent the smuggling of arms to protesters.
Police will use live ammunition to subdue any attack against police facilities, state media said.