At least 74 people have been killed in clashes between rival fans following a football match in the Egyptian city of Port Said.
Scores were injured as fans - reportedly armed with knives - invaded the pitch after a match between top-tier clubs al-Masry and al-Ahly.
The Egyptian government said it is the biggest disaster in the country's football history.
A statement posted on the Supreme Council of the Armed Forces' Facebook page announced three days of national mourning, beginning today.
The statement also promised a full investigation into the incident.
All premier-league matches have been cancelled and the newly-elected Egyptian parliament is to hold an emergency session today.