The attacks took place in the wee hours after militants stormed some army checkpoints in Al-Arish and Sheikh Zwayed cities in North Sinai, prompting security forces to retaliate in which 15 militants were killed and as many soldiers found dead, Egyptian army said in a statement.
Two civilians were also killed while 19 others sustained injuries in the attack, it added.
The militants attacked the checkpoints with rocket- propelled grenades and heavy weapons, local media quoted security sources as saying, adding that the army has launched airstrike following the attacks.
The injured were transferred to a nearby military hospital for treatment.
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Egypt's Sinai has witnessed many violent attacks by militants since the January 2011 revolution that toppled the ex-president Hosni Mubarak.
The attacks targeting police and military increased after the ouster of Islamist ex-president Mohamed Morsi in 2013.
Over 500 security personnel have been reported killed since then.
The military has launched security campaigns in the area, arrested suspects and demolished houses that belong to terrorists, including those facilitating tunnels leading to the Gaza Strip.