FIFA has demanded a full report into the violence at match in Egypt on Wednesday night that left more than 70 people dead.
Death toll rises to 74 after Egyptian football riot
Al Masry fans invaded the pitch after a surprise 3-1 win over Cairo club Al-Ahly in Port Said, 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 has now 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, Sepp 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."