A senior Interior Ministry official denied that security forces had used birdshot to disperse the protest. Prime Minister Ibrahim Mahlab said Sabbagh’s death was being investigated and that “whoever committed a mistake will be punished.”

At least 19 others were killed across Egypt over the weekend in the bloodiest day since Abdel Fattah El-Sisi was elected president in June 2014 after leading a military coup against the Muslim Brotherhood-backed and democratically elected president Mohammed Morsi the year before. Most were protesters. However, Egypt's Interior Ministry counted two alleged militants attempting to detonate a bomb under an electricity tower in Damanhur, near Alexandria, among the dead.

Security forces and plain-clothed police fired munitions at protesters, witnesses said. As night fell in Cairo, gunfire and sirens could be heard as armored personnel carriers moved through the city.

For their part, protesters set fire to a government building near the Pyramids. Authorities reported that gunmen killed two policemen at a security checkpoint near the historical site. However, the gunmen’s affiliation wasn’t clear.

The heaviest death toll among protesters was seen in Matariya, a Cairo suburb and stronghold of the Muslim Brotherhood. Witnesses said security forces fired on protesters. Eight people, including one policeman, were killed in the suburb, according to the Health Ministry.

Though four years of political and economic turmoil followed Mubarak’s ouster, many Egyptians have ignored allegations of human rights abuses and repression and praised Sisi for restoring stability in Egypt — a strategic ally of the U.S.

But some, especially young Egyptians, showed signs of discontent on the revolution’s anniversary — taking to the streets to demand democratic reforms.

“The situation is the same as it was four years ago and it is getting worse. The regime did not fall yet,” said Alaa Lasheen, a 34-year-old engineer.

Human rights groups have accused Sisi of authoritarian rule, though he has claimed he is committed to democracy. Other critics said new laws, including one restricting protests, have taken away hard-won freedoms from the uprising. Scores of Islamist and liberal activists, as well as journalists, have been jailed since Sisi took power in a military coup from Egypt's first democratically elected president Mohamed Morsi in 2013.

In a pre-recorded speech aired on state television hours after Sabbagh’s deah, Sisi marked the anniversary of the revolution, saying: “I salute all our martyrs, from the beginning of January 25 [2011] until now.”

Meanwhile, an Egyptian court ordered the release of Mubarak’s sons Alaa and Gamal on Thursday pending a retrial in a corruption case. Charges against Mubarak for conspiring to kill protesters during the revolution were dropped by a court in November — in yet another sign that the old guard was returning to power in Egypt.

With wire services