Clashes between supporters and opponents of Mohamed Morsy killed four people on Monday as the ousted Egyptian president's family vowed to sue the army over his ouster.
At least 26 people were also injured as the rival camps exchanged volleys of stones and birdshot, emergency services said.
Police fired tear gas in a bid to disperse the clashing demonstrators.
The fresh violence came as Morsy's family said they planned to sue the military for having "kidnapped" the elected president, who has been in custody since the 3 July coup.
It came despite an appeal by the army-installed civilian caretaker government for demonstrators to show restraint after weeks of nationwide demonstrations and deadly violence in the Sinai Peninsula.
Shaimaa Mohamed Morsy, the toppled president's daughter, told a news conference that the family was planning to take legal action in Egypt and abroad.
"We are taking local and international legal measures against Abdel Fattah al-Sisi, the leader of the bloody military coup, and his putschist group," she said of the army chief.
She voiced dismay at "the silence of rights organisations and civil society over the crime of kidnapping the legitimate president," whose election in June last year was widely regarded as Egypt's first free vote for a leader.
The family held General Sisi responsible for Morsy's safety.
Morsy has been detained at an unknown location since his overthrow.
Morsy's son Osama said the family had not heard from him since. "None of us has had any contact with our father since the afternoon of the coup on July 3," he told reporters.
The United States and Germany have led international calls for Morsy's release, but Egypt's interim authorities have rejected them, saying he is being held in a "safe place".
Supporters of Morsy, who was ousted after a single year of his mandate, have pressed demonstrations, holding marches and protests across the country since his fall.
Some have led to bloody clashes and on Monday security and medical sources reported at least four people dead and 26 wounded.
One was killed near Cairo's Tahrir Square, epicentre of the 2011 uprising that ended three decades of autocratic rule by Hosni Mubarak.
Three more died in Qalyub, in the northern outskirts of the capital.
Large crowds of Morsy supporters had held protests calling for his reinstatement.
Members of the now dissolved upper house of parliament, which had been dominated by Morsy's Islamist backers, held a defiant meeting in Cairo's Rabea al-Adaweya mosque.
Chanting "Sisi killer," and anti-police slogans, demonstrators also hung pictures of the ousted president on the gates of the public prosecutor's office.
"I believe we will restore him by more pressure on the streets," Mohammed Awad, one of the protesters, told AFP.
Others at the march dismissed the legitimacy of the new interim authorities.
Supporters of Morsy also rallied in the Abbaseya area of Cairo, near the defence ministry.
On Sunday, the cabinet meeting focused on Egypt's battered economy and efforts to boost the deteriorating security situation.
Since Morsy's ouster, militants have ratcheted up attacks on security forces in the restive Sinai, killing four security services personnel and two civilians on Sunday.
Assailants shot dead the three soldiers and one policeman in separate attacks in Arish, and two civilian bystanders were killed later when the army traded fire with gunmen, security sources told AFP.
In Rafah, a Sinai town that straddles the border with the Gaza Strip, unknown assailants launched an attack on a riot police camp with mortars and rocket-propelled grenades, wounding five policemen.
Analysts attribute the Sinai violence to Islamist militants seeking to take advantage of the insecurity that has followed Morsy's ouster.
