The sound of heavy gunfire rang out across the square as armed security forces charged hundreds of protesters attempting to hold their ground, activists and a Reuters witness said.

"Hundreds of state security forces and the army entered the square and began firing heavily. They chased protesters and burned anything in their way, including medical supplies and blankets," protester Ismail said by telephone.

Before the latest security charge, protesters had been trying to tear down a brick wall the army had put up to block access to parliament, which is located beside the square.

A security source told Reuters some protesters wanted to remove the wall in order to reach parliament and destroy it.

Medical sources have said 13 people have been killed since Friday, but the protesters say the latest attack produced more casualties. "Some of those who fell had gunshot wounds to the legs," Ismail said.

Hundreds more were wounded and scores have been detained in attempts to disperse protests in and around Tahrir Square, hub of the uprising that ousted Hosni Mubarak in February.

Anger has been inflamed by brutal attacks on protesters at the weekend, including one on a young woman whose clothes were partly torn off, captured on video for the world to see.

Meanwhile, in an interview with the BBC, Robin Wright, a senior fellow at the US Institute of Peace, said the SCAF regime was now effectively a military junta preventing the country from moving forward and the protests were taking on the form of a real revolution.

For videos see:
 http://vastminority.blogspot.com/2011/12/tuesday-dawn-raid-on-tahrir-square.html