Abdel-Fattah el-Sissi spoke during a televised address today in a ceremony marking the birthday of Islam's Prophet Muhammad.
The massacre, which took place as worshippers were praying in a village mosque on Friday, was the deadliest terrorist attack in Egypt's modern history.
El-Sissi authorised his new chief of staff, Maj. Gen. Mohammed Farid Hegazy, to use "all brute force" against the militants, who have been battling security forces in Sinai for years.
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