Egypt's President Abdel-Fattah el-Sissi says a deadly assault on an army checkpoint in the Sinai Peninsula that killed 30 troops was a "foreign-funded operation."

Roaring in front of cameras on Saturday, el-Sissi said there are foreign powers that want to "break the back of Egypt," without elaborating. He vowed to take drastic measures to uproot the militants and said Egypt is engaged in an "extensive war" that will last a long time.

"There is a big conspiracy against us," he said while standing with army commanders ahead of a military funeral for the slain soldiers and officers.

Egypt declared a state of emergency and imposed a three-hour curfew in the restive northern part of the peninsula after Friday's assault. No group has yet claimed responsibility for the attack.