At least 17 people have been killed in unrest in Egypt as the country marked the fourth anniversary of its 2011 uprising, state media are reporting.

The interior ministry said a policeman was shot dead in clashes with Islamist protesters in a north Cairo neighbourhood that also killed a number of demonstrators.

It is not clear at this stage whether the policeman was included in the toll of 17 people reported by the state-owned Al-Ahram newspaper on its website.

Another Islamist protester was shot dead in clashes with police in the Mediterranean city of Alexandria. Officials said he was killed after he opened fire and police responded.

In central Cairo, police fired shotguns and tear gas to disperse hundreds of protesters who tried to march on the central Tahrir Square, the epicentre of the early 2011 revolt that ousted then-president Hosni Mubarak.

Egypt had already tightened security ahead of the anniversary of the popular uprising.

Security sources said a woman protester was shot dead yesterday 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 yesterday, President Abdel Fattahal-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".

Mr 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 Alaaand 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.