At least 17 people were killed on Sunday in Egypt's bloodiest protests since Abdel Fattah al-Sisi was elected president, as security forces fired at protesters marking the anniversary of the 2011 uprising that toppled Hosni Mubarak.
Gunfire and sirens could be heard in Cairo into the night as armoured personnel carriers moved through the centre of a city where security forces had once again used lethal force against dissenters. A health ministry spokesperson said at least 17 people had been killed at protests across the country.
The anniversary was a test of whether Islamists and liberal activists had the resolve to challenge a government that has persistently stamped out dissent since the then-army chief Sisi ousted elected Islamist president Mohamed Mursi in July 2013 after mass protests against his rule.
Gunmen in a car opened fire on a security checkpoint near the pyramids, killing two policemen, and a bomb wounded two policemen outside a Cairo sports club, security sources said.
During the day, riot police backed by soldiers in armoured vehicles sealed off roads, including those leading to Cairo's Tahrir Square, the symbolic heart of the 2011 revolt.
The heaviest death toll was in the Cairo suburb of Matariya, a Muslim Brotherhood stronghold. Special forces fired pistols and rifles at protesters, a Reuters witness said. Eight people, including one policeman, were killed, the health ministry said.
People in Matariya chanted "down with military rule" and "a revolution all over again". Some threw Molotov cocktails at security forces and fires raged in the streets.
In downtown Cairo, riot police with rifles and plain clothed men with pistols chased protesters through the streets.
Six people were killed in separate protests in Alexandria, Egypt's second biggest city, Giza governorate outside of Cairo and the Nile Delta province of Baheira, security sources said.
Signs of discontent built up as the anniversary of the revolt against Mubarak approached, and a liberal woman activist, Shaimaa Sabbagh, was shot dead at a protest on Saturday.
About 1,000 people marched in her funeral procession on Sunday. The Health Ministry said she had been shot in the face and back and Interior Ministry spokesperson Hany Abdel Latif said an investigation into her death had begun, adding: "No one is above the law."
"Shaima was killed in cold blood," Medhat al-Zahid, vice president of the Socialist Popular Alliance party that Sabbagh belonged to, told a news conference.
Sisi's crackdown has neutralised the Brotherhood but failed to end an Islamist insurgency in the Sinai Peninsula near the Israeli border.
A curfew imposed in north Sinai was extended for three months, authorities said. Islamist militants based in the Sinai have killed hundreds of police and soldiers since Mursi's removal. They have pledged support for Islamic State, the ultra-hardline group that seized parts of Iraq and Syria.
After four years of political and economic turmoil following Mubarak's fall, many Egyptians have overlooked allegations of widespread human rights abuses and praised Sisi for restoring a measure of stability.
Sisi, who served as military intelligence chief under Mubarak, has also taken bold steps to repair the economy, such as cutting costly fuel subsidies.
But his critics accuse him of restoring authoritarian rule and repealing freedoms won in the uprising that ended three decades of iron-fisted rule under Mubarak.
"The situation is the same as it was four years ago and it is getting worse. The regime did not fall yet," said engineer Alaa Lasheen, 34, protesting near Tahrir Square.
In a televised address on Saturday, Sisi praised the desire for change that Egyptians showed four years ago but said it would take patience to achieve all of "the revolution's goals".
Sheikh Youssef al-Qaradawi, an Egyptian-born cleric based in Qatar who supports the Brotherhood, said Mursi was Egypt's legitimate leader.
Qaradawi's outspoken support for the Islamist movement has fuelled a diplomatic rift between Qatar and its Gulf Arab allies which, like Cairo, consider the group a security threat.