CAIRO - Egypt tightened security on Sunday, the anniversary of the popular uprising that toppled autocrat Hosni Mubarak in 2011.
A Reuters witness heard an explosion in the Alf Maskan area of Cairo. Security officials were not immediately available for comment.
Security sources said a woman protester was shot dead on Saturday near Cairo's Tahrir Square, the symbolic heart of the revolt that ended Mubarak's 30 years of rule. Dozens of protesters were killed during last year's anniversary.
State news agency MENA said 22 armoured vehicles were parked around Tahrir Square and roads to the square were sealed off.
Security forces were also dispatched to Rabaa Square in northeast Cairo, where hundreds of supporters of Islamist President Mohamed Mursi were killed in August 2014, one month after the army toppled him.
Although a security crackdown has virtually ended street demonstrations, several took place this week in Cairo and Egypt's second city, Alexandria.
In a televised address on Saturday, President Abdel Fattah al-Sisi praised the desire for change Egyptians showed four years ago but said it would take patience to achieve all of "the revolution's goals".
Sisi has moved to improve Egypt's economy, and he announced a roadmap to democracy after toppling Mursi when mass protests against his rule erupted. But he served as military intelligence chief under Mubarak, and 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, when hundreds died as security forces clashed with protesters. Islamists and liberal activists, including many who supported removing Mursi and his Muslim Brotherhood, have been jailed.
Mubarak-era figures are slowly being cleared of charges and laws curtailing political freedoms have raised fears among activists that the old leadership is regaining influence.
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.