Three were killed on Friday and scores injured when supporters of ousted Islamist president Mohamed Morsi clashed with police and opposing civilians in Cairo and elsewhere, the health ministry said.
Security forces fired teargas to disperse protests that descended into violence in several cities.
At least 28 people were injured in clashes -- in which stones, firebombs, and birdshot pellets were used -- in cities incluidng Cairo, Alexandria, the Nile Delta's Sharqiya and Fayoum, according to the health ministry.
Police said 47 people were arrested throughout the day.
Fierce clashes erupted in northeast Cairo when several thousand Brotherhood supporters fought with police and civilian opponents in the Alf Maskan area of Ain Shams, leaving at least one dead and several injured, a security source told Ahram Online.
Police fired heavy rounds of teargas to disperse the crowds, and eyewitnesses said live rounds were fired by both sides.
"Police forces handled armed assailants in Cairo's Ain Shams district – who indiscriminately fired live rounds and birdshots – with great caution, fearing for the safety of residents," the interior ministry said in a statement.
Islamists have tried to regalvanise their flagging street movement amid an intense security crackdown that has killed hundreds and led to thousands of arrests since Morsi's ouster in July.
Egyptian authorities declared the Brotherhood a terrorist group late last year, accusing it of links to Islamist militants who had stepped up their attacks, mostly against police and army targets, since Morsi's removal. The designation was confirmed by a court ruling last week.
The group vehemently denies any links to violence.
A pro-Morsi grouping, led by his Brotherhood movement, called for a week of protests beginning on Friday to condemn the killing and detention of protesters.
The National Alliance to Support Legitimacy said the protests would also condemn a presidential candidate backed by the "Americans and the Zionists," in reference to army chief Abdel-Fattah El-Sisi.
El-Sisi, who has become a cult figure since he led Morsi's ouster, is tipped to handsomely win if he stands in a presidential vote slated for the summer.
In Fayoum, five people were injured, including a woman and a policeman, as birdshots and fireworks were used in clashes. Brotherhood supporters set fire to tires, and police fired heavy rounds of teargas to disperse crowds protesting in the city centre.
Three policemen suffered burns when unknown assailants set alight two police vehicles in Giza's Faysal district, Al-Ahram Arabic news website reported.
And in Fayoum, two private cars owned by police officers were set ablaze by unidentified assailants.
Four policemen were wounded with birdshot during violence in Suez governorate, an interior ministry spokesman said.
In Sharqiya's Zagazig, police fired teargas to disperse crowds of protesters for and against Morsi who fought using sticks, stones and birdshot, leaving at least six injured, state news agency MENA reported.
Forty seven people were arrested nationwide on Friday -- including a militant suspect in Fayoum -- for rioting and assaulting civilians, the interior ministry said. Twelve other Brotherhood members who were issued arrest warrants were also apprehended.
Morsi, Egypt's first freely elected president, was ousted by the army last summer after millions protested against his turbulent year-long rule. Critics accused his Brotherhood group of power-grabbing and sending an already ailing economy into a nosedive.
The deposed leader faces a number of trials on a wide array of charges, including inciting the murder of opposition protesters, espionage and a jailbreak during the 2011 uprising.
Most of the Brotherhood's senior leaders are behind bars, with some standing trial on the same charges as Morsi, some of which carry the death penalty.
The clampdown on Islamists has recently extended to secular-minded activists and there have been allegations of torture against the police, causing many to fear a diminishing tolerance for dissent by the government.
An Islamist insurgency in the border Sinai Peninsula, which has recently spread to other parts of the country, has killed hundreds of police and soldiers in recent months.