Attackers armed with knives have clashed with pro-democracy demonstrators in Cairo. The incident took place on Wednesday at Tahrir Square, the epi-centre of anti-Government protests that toppled President Hosni Mubarak. Television video from the Square showed the two sides throwing rockets at each other The unrest erupted after hundreds of pro-democracy activists gathered for a rally at the Square. Meanwhile, Egyptian officials say the death toll from violent clashes Tuesday between Muslims and Christians has risen to 13.