Fifa has demanded a "full report" into the violence in Egypt which has left more than 70 people dead.It has asked the Egyptian authorities to explain exactly what happened following the match between Al-Ahly and Al Masry on Wednesday.Fifa president Sep Blatter has written to Egyptian FA president Samir Zaher."Today is a black day for football and we must take steps to ensure that such a catastrophe never happens again," wrote Blatter."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."Senior officials in the Egyptian city of Port Said, where the deaths occurred, and the national football association have already been sacked.The governor of Port Said has resigned, while two senior security officials have been suspended and are in custody.Three days of national mourning have been declared.A minute's silence will be held before this weekend's quarter-final matches at the Africa Cup of Nations in Gabon and Equatorial Guinea.Confederation of African Football president Issa Hayatou, whose organisation is based in Cairo, told www.cafonline.com : "African football is in a state of mourning."