Egypt tightened security on Sunday on the anniversary of the popular uprising that toppled autocrat Hosni Mubarak in 2011.
State news agency MENA said 22 armored army vehicles were stationed around Cairo's Tahrir Square, the symbolic heart of the revolt that ended 30 years of iron-fisted rule under Mubarak and raised hopes of greater freedoms.
Roads leading to the square were sealed off.
Although a security crackdown since 2013 ,when the army toppled Islamist president Mohamed Mursi, has virtually ended street demonstrations, several took place this week in Cairo and Egypt's second city Alexandria.
A woman protester was shot dead near Tahrir Square on Saturday, security sources said. During last year's anniversary of the uprising, dozens of protestors were killed.
In a scheduled televised address on Saturday evening, President Abdel Fattah al-Sisi praised the desire for change demonstrated by Egyptians four years ago, but said it would take patience to achieve all of "the revolution's goals".
While former army chief Sisi has taken steps to improve Egypt's economy, human rights groups accuse him of restoring authoritarian rule to the most populous Arab state.
Opponents say new laws, including one restricting protests, have rolled back freedoms won in the uprising. Islamists and liberal activists, including many who supported the removal of Mursi and his Muslim Brotherhood movement, have been jailed.
The government says it is committed to democracy.
Sisi, who served as military intelligence chief under Mubarak, toppled Mursi after mass protests against his rule and announced a political roadmap to democracy.
An Egyptian court ordered the release of Mubarak's sons Alaa and Gamal on Thursday pending a retrial in a corruption case.
In November, a court dropped charges against Mubarak of conspiring to kill protesters in the uprising.
Mubarak-era figures are slowly being cleared of charges and a series of laws curtailing political freedoms have raised fears among activists that the old leadership is regaining influence.
Hundreds of people died when security forces clashed with protesters in the weeks before Mubarak was forced from power.