El-ARISH, Egypt — Egypt's President Abdel Fattah el-Sissi told his nation to prepare for a long fight to defeat Islamic extremists Saturday following a wave of attacks on security forces in the Sinai Peninsula.

El-Sissi made his televised address as military commanders announced plans to forge a unified command for all armed forces in Sinai.

"We will not leave Sinai for the terrorists," el-Sissi said.

Extremists targeting Egyptian military positions killed 31 security force members in a sophisticated and multi-pronged set of attacks Thursday night.

An Islamic State-linked group in Egypt claimed responsibility, but el-Sissi laid the blame on the Muslim Brotherhood, the Islamist movement he ousted from power in 2013.

The Egyptian government has long said it is fighting a war on terror. But it has not been able to stem a daily stream of militant attacks despite more than a year of massive military operations in northern Sinai.

Two children, aged 6 and 6 months, were killed Friday in an explosion that the army blamed on the militants.

A military official said the new "unified command" will mean joining the army units in North and South Sinai into a single force. He said this will involve setting up a new headquarters in El-Arish to administer military operations against terrorism.

The official spoke on condition of anonymity because he was not authorized to speak to reporters.

Thursday's assault was the second major deadly attack on Egyptian security forces in Sinai in the last 6 months. 31 troops were killed in an attack last October.

Attacks on Egyptian security forces dramatically escalated after the military — led by el-Sissi — ousted Islamist President Mohammed Morsi in July 2013.