Riot police using tear gas broke up protests which were set to continue through the night with the aim of securing President Mubarak's stepping down from the position he has held since 1981.
Activity in Cairo yesterday saw thousands of protesters meet at Tahrir Square, a major public square close to the Parliament building.
The protests, organised via Facebook, have been inspired by the uprising in Tunisia.
Twitter users have also been involved, issuing news posts relating to the protests.
A fourth person has died overnight in Suez. Two other protesters and a policeman have been killed in the clashes.
The Egyptian stock market has seen a drop over more than four percent following the protests.
An interior ministry release has been issued banning the demonstrations.
The document states that anyone involved in protests, and other "unauthorised action" will be detained and prosecuted.
Reports today state that protesters have nonetheless begun gathering again this morning, despite the ban and despite statements by security forces saying that protesters will not be allowed to assemble again today.