The Egyptian military is being deployed to the Mediterranean city of Port Said after eight people were killed in riots outside the main prison.
The rioting followed a controversial verdict related to one of the world's deadliest incidents of football violence, Egyptian officials said.
A Cairo judge sentenced 21 people to death in connection with the February 1 2012 football violence in Port Said that killed 74 fans of the Cairo-based Al-Ahly team.
Two police were shot dead outside Port Said's main prison when angry relatives tried to storm the facility to free the defendants on trial.
Police fired tear gas and rubber bullets at the crowd, killing six.