Egyptian security forces have fired teargas at thousands of protesters, some of whom threw stones, in Cairo's Tahrir Square, reports Al Jazeera.

The clashes were apparently triggered by relatives of the more than 840 people who were killed during the Egyptian uprising in February.

The protesters - 3,000 of them - once again gathered at Tahrir Square, which was the center of the nearly three-week-long uprising that overthrew former president Hosni Mubarak.

Al Jazeera's Ayman Mohyeldin reporting from Cairo said at least eight people have been injured: "Police have been using teargas to try and disperse the crowd and push them back."

Ahram Online reports that a statement released by the interior ministry of Egypt has denied that police attacked protesters and claimed they were thugs.

The website says Egyptian TV channels Al Hayat and On TV aired live footage of the clashes, which showed Tahrir square and surrounding downtown streets "looked like a battlefield covered with a smoky cloud of tear gas".

It is reported that the protesters at Tahrir Square are calling for the removal of Hussein Tantawi, the head of the Supreme Council of the Armed Forces, which took power when Mubarak stepped down.

Families of those killed are reportedly frustrated with what they say is the slow prosecution of security officers believed responsible for the deaths of protesters during the uprising.

No officials or security force members have been charged with the killing of the protesters.