Tahrir Square

Earlier, witnesses said thousands of pro-Mubarak supporters had entered the square. Opposition groups said Mubarak had sent in thugs to suppress the protest.

Also in Cairo, Al Jazeera's Jane Dutton, said that "hundreds of anti-government supporters were running from the square, including many women and children".

Fighting took place around army tanks deployed around the square, with stones bouncing off the armoured vehicles. Soldiers did not intervene.

Several groups were involved in fist fights, and some were using clubs.  The opposition also said many among the pro-Mubarak crowd were policemen in plainclothes.

"Members of security forces dressed in plain clothes and a number of thugs have stormed Tahrir Square," three opposition groups said in a statement.