The assault came on the second day of clashes between Egyptian security and protesters calling on the ruling military to quickly announce a date for the transfer of power to a civilian administration.
Doctors at nearby hospitals said a total of three men were reported dead as a result of the clash. Hundreds have also been wounded.
An estimated 5,000 protesters have been in and around Tahrir Square, the birthplace of the uprising that toppled Hosni Mubarak in February.
The Associated Press contributed to this story.