Most of the terror attacks were carried out by a Sinai-based group affiliated with the Islamic State (IS) regional terrorist group.
According to the spokesman, eight soldiers were killed and 15 others injured when some of the attackers detonated their explosive vests. It did not say how the other nine were killed.
Egypt's Sinai Peninsula has been the centre of terrorist attacks that have killed hundreds of policemen and soldiers following the military ouster of former Islamist President Mohamed Morsi in July 2013.
The security forces have arrested suspects and demolished houses that belong to terrorists, including those facilitating tunnels leading to the Gaza Strip.
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More than 100 militants and at least 22 soldiers have been killed in an ongoing operation launched on February 9 against the militants, according to army figures.
Egypt first imposed the current state of emergency in April 2017 after two church bombings killed at least 45 people. According the Egyptian constitution, a state of emergency can not exceed six months from its date of declaration and decrees imposing or extending it should be approved by the parliament.
The latest extension was to allow security forces to "take [measures] necessary to confront the dangers and funding of terrorism and safeguard security in all parts of the country", the official gazette said.
The state of emergency includes a curfew in parts of North Sinai from 7pm until 6am, except in El-Arish city and on the worldwide road, where the curfew is in effect from1am to 5am.