At least two Egyptian soldiers were killed in a massive explosion at Egyptian security headquarters in the southern Sinai town of al-Tor, al-Arabiya reported. More than 50 were injured in the blast, which officials suspect was caused by a car bomb, the pan-Arab network said.
Earlier, five Egyptian soldiers were killed by gunmen in Ismailia, al-Arabiya said. The BBC reported the soldiers were sitting in a car at a checkpoint north of Ismailia when they were killed. The British network also said a rocket hit a satellite station in a Cairo neighborhood. There were no details concerning casualties.
Al-Arabiya said the death toll from Sunday's violence rose to 53, describing it as one of the bloodiest days since former President Mohamed Morsi's July 3 ouster.
An Egyptian group formed to protest the military regime that ousted Morsi called for fresh protests.
The Islamist Anti-Coup Alliance called on followers to take to the streets Tuesday and Friday after Sunday's bloody melee that the Interior Ministry said left at least 268 people injured and more than 460 arrested.
Egypt is under an extended nationwide state of emergency that includes the suspension of most rights afforded criminal suspects.
The state of emergency was imposed Aug. 14, the day police stormed two Islamist sit-ins against the country's military takeover and killed more than 600 protesters. It was extended Sept. 13 for two more months because of the country's continued strife, state-owned newspaper al-Ahram reported at the time.
Sunday's violence started when thousands of anti-coup protesters tried but failed to bring their protest into iconic Tahrir Square where thousands of pro-regime demonstrators were voicing support for the army during a 40th anniversary celebration of an Egyptian victory over Israel in the 1973 Arab-Israeli War.
The anti-coup protesters Sunday were repelled by swarms of police, tear gas and gunfire, The Washington Post, The New York Times and al-Ahram reported.
The death toll was the highest in a single day since mid-August, when military-led authorities began a crackdown on Morsi supporters.
"Closing roads, blocking entries to public squares and stopping trains and metro lines will never prevent the world from seeing the truth," the alliance said in a statement Sunday night.
The group said it would hold the state accountable for the deaths and vowed it would "pursue and prosecute" those responsible.
"God save the honorable people of Egypt," the statement said.
The possibility of Sunday's bloody confrontation started last week when the anti-coup protesters said they intended to go to Tahrir to salute "the soldiers who fought the October war -- so our brave army regains its commitment to the true Egyptian military doctrine and knows the difference between the enemy and its people, before it turns into militias that do not have any other mission but killing its own people."
That announcement prompted the military-led regime to respond with the Tahrir military commemoration.
A spokesman for Egypt's presidency said Saturday anyone protesting the military Sunday would be considered a foreign agent.
Pro- and anti-regime violence was also sparked in other cities, al-Ahram said, with deaths reported in Giza, Beni Suef, 70 miles south of Cairo, and in Minya, 160 miles south.