CAIRO (Reuters) - Two policemen were shot dead outside a prison in Egypt's Port Said on Saturday shortly after a court sentenced to death 21 people found guilty over a 2012 soccer stadium disaster that killed 74 people, a security source reported.

Protesters had gathered at the prison where many of the defendants in the soccer case were held and state media had earlier reported gunshots outside the jail.

Earlier on Saturday, a court sentenced to death 21 of the 73 defendants accused in the Port Said soccer stadium disaster.

Soccer fans and families in Cairo had cheered the court ruling. Soccer supporters had demanded the death penalty for the accused and threatened violence if justice was not done.

But some in Port Said were angry that people from their city were being held responsible for the disaster, and many rampaged through the streets. A witness saw some storming a police station.

(Reporting by Yasmine Saleh; Writing by Edmund Blair; Editing by Janet Lawrence)