Cabinet spokesman Sherief Shawki blamed the blast on theMuslim Brotherhood group of former Islamist President MohamedMorsi, and said Prime Minister Hazem el-Beblawi had officiallydeclared the group a terrorist organisation.
A security source said the blast may have been caused by acar bomb, but it was not clear if it was suicide attack or not.
State TV said at least 11 people were killed and more than100 hurt. It said the attack was the worst in the city's historyand two senior security officials were among the wounded.
Another security source it was still unclear what caused theexplosion, "but it seems to be a big one that led to thecollapse of parts of the security building."