Egyptian opposition leader Mohamed ElBaradei has been placed under house arrest.
The Nobel Peace Laureate returned to the country on Thursday from a month abroad and declared he was ready to lead the protesters towards regime change.
Police stationed outside his suburban Cairo home have told him he cannot leave the house after he joined tens of thousands of protesters in the capital.
Friday saw crowds throw stones at police, who fired back with rubber bullets and tear gas, in the most violent and chaotic scenes yet in the challenge to President Hosni Mubarak's 30-year rule
Egyptian military vehicles were seen on the streets of Cairo on Friday afternoon, according to reports.
Protesters have chanted slogans calling for the army to support them, shouting: "Where is the army? Come and see what the police is doing to us. We want the army. We want the army."
A crowd carried the body of a protester through the city of Suez after clashes with police who withdrew from central areas of the eastern city, leaving some main streets in the hands of demonstrators.
"They have killed my brother," shouted one of the group.