FIFA today demanded a full report into the violence at match in Egypt last night that left more than 70 people dead.
Al Masry fans invaded the pitch after a surprise 3-1 win over Cairo club Al-Ahly in Port Said last night, with reports stating as many as 79 people died in the ensuing violence.
There have been claims that security forces and police did not do enough to intervene, and that the violence was tied up with the political power struggle in the country. FIFA, the game's world governing body, today asked the Egyptian authorities to explain exactly what happened.
FIFA said in a statement: "FIFA has asked the Egyptian authorities for a full report on the incidents in order to evaluate what happened."
In a letter to Egyptian FA president Samir Zaher, the world governing body's president Blatter offered support and said: "Today is a black day for football and we must take steps to ensure that such a catastrophe never happens again.
"Football is a force for good and we must not allow it to be abused by those who mean evil.
"I await further news from you concerning the circumstances of this tragedy."
Home fans reportedly armed with sticks and knives stormed the field after the final whistle.
Reports suggest some Al-Ahly fans suffocated, trapped in a narrow corridor as they fled the violence.
Al-Ahly's Portuguese coach Manuel Jose has returned to Portugal to ponder his future after being attacked, while his assistant coach Pedro Barny backed up the claims that security staff did too little.
Jose told www.el-ahly.com: "I was beaten with fists and kicks to the neck, head and feet. I saw our fans die before us and we are unable to do anything."
Assistant coach Barny added: "What happened was an unspeakable catastrophe.
"From the beginning of the game, the fans of the opposing team's fans were allowed to fire rockets and stones at us without any intervention.
"In the end, it turned into a state of madness without any role for the security in the stands.
"We tried to save the lives of some of the fans, but many died before our eyes."
The Egyptian Football Federation last night announced an indefinite suspension of all leagues in the country following the trouble.
Meanwhile, reports in Egypt have stated Al Masry president Kamel Abu Ali has resigned.
A minute's silence will be held before this weekend's quarter-final matches at the African Nations Cup in Gabon and Equatorial Guinea.
Confederation of African Football president Issa Hayatou, whose organisation are based in Cairo, told www.cafonline.com: "African football is in a state of mourning."