Egypt launched air strikes on militant targets in the Sinai peninsula on Thursday, killing 23 fighters a day after the deadliest clashes in the region in years, security sources said.

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 the self-proclaimed Islamic State of Iraq and Sham (ISIS), have stepped up attacks on soldiers and police since then-army chief Abdel Fattah al-Sissi toppled democratically-elected President Mohamed Morsi in 2013 after mass protests.

Sissi, now Egypt's president, says the pro-ISIS 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 U.S. 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.

Meanwhile on Wednesday, 13 leaders of Muslim Brotherhood of former President Morsi, were killed in a house raid.