The sources said those killed had taken part in Wednesday's fighting in which 100 militants and 17 soldiers, including four officers, were killed, according to the army spokesman.
Sinai-based insurgents, affiliates of Islamic State, have stepped up attacks on soldiers and police since then-army chief Abdel Fattah al-Sisi toppled Islamist President Mohamed Mursi in 2013 after mass protests against his rule.
Sisi, now Egypt's elected president, says the pro-Islamic State group Sinai Province, and other militant factions, pose an existential threat to Egypt, other Arab states and the West.
This week has been especially troubling for Egypt, a strategic US ally which has a peace treaty with Israel and controls the Suez Canal, a vital global shipping lane.
The militants' assault, a significant escalation in violence in the peninsula between Israel, the Gaza Strip and the Suez Canal, was the second major attack in Egypt this week.
On Monday, a car bomb killed the prosecutor-general in Cairo, the highest-profile official to die since the insurgency began.
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