Cairo, Egypt (CNN) -- Police fired tear gas and rubber bullets early Wednesday to break up a demonstration by relatives of those killed in Egypt's revolution.

Clashes in Cairo's Tahrir Square between protesters and authorities have left at least 26 officers injured, the Ministry of Interior said.

In addition, at least five protesters were wounded in the tear gas and rubber bullet firing, and ambulances continued to transport protesters to medical attention. Some demonstrators were throwing rocks.

About 1,000 people turned out Tuesday night to commemorate the victims of the January-February uprising that drove longtime Egyptian strongman Hosni Mubarak from power. Police began using tear gas on demonstrators who would not leave the square.

Authorities were trying to block entrances to the area, as more people were being asked on the Internet to join the protesters.

At least five people were seen bleeding from their heads amid the clashes, which continued into Wednesday's early-morning hours.

The human rights group Amnesty Amnesty International has estimated at least 840 people were killed and more than 6,000 wounded during the three-week revolution. The military-led government that took over when Mubarak resigned has been prosecuting several former officials accused of ordering security forces to fire on protesters.

A police officer accused of killing 20 protesters during a January 28 demonstration has been sentenced to death, and ex-Interior Minister Habib El Adly faces capital charges in the deaths of demonstrators. El Adly and other officials in Mubarak's government have also been convicted on corruption charges, and the ailing Mubarak could be put on trial as well.

Egypt's military rulers have set parliamentary elections for September, and an administrative judge ordered the dissolution of local city councils that anti-Mubarak activists had denounced as corrupt. But sporadic protests have continued in the months since Mubarak's ouster as Egyptians have demanded speedier reforms and economic improvements.

Journalist Mohamed Fadel Fahmy contributed to this report.