The Egyptian authorities are battling an insurgency by the Islamic State (IS) group in North Sinai that has killed hundreds of members of the security forces.
The military did not specify to which group the 30 extremists belonged but described them as "extremely dangerous".
Five others were arrested as Egyptian forces imposed a "tight siege" on the North Sinai provincial capital El-Arish and the cities of Sheikh Zuweid and Rafah, a military statement said.
Egypt has struggled to quash attacks led by IS, whose local branch is based in North Sinai, after the army ousted Islamist president Mohamed Morsi in 2013.
The bombing by IS of a Russian airliner carrying holiday makers from a South Sinai resort in 2015 killed all 224 people on board and severely damaged the country's tourism sector.
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