At least 23 Egyptian soldiers were killed when two suicide car bombs tore through military checkpoints in North Sinai province on Friday, security sources said, in one of the bloodiest coordinated assaults on security forces in years.Islamic State militants are waging an insurgency in the rugged, thinly populated Sinai Peninsula. They have killed hundreds of soldiers and police since 2013, when the military ousted Islamist President Mohamed Mursi after mass protests against his rule.The two cars blew up as they passed through two checkpoints outside of a military compound just south of Rafah, on the border with the Gaza Strip, the security sources said. No group claimed responsibility for the attacks.The security sources said another 26 soldiers were injured in Friday's attacks. The military put the casualties lower, saying the attacks had killed and injured a total of 26 soldiers, without providing a breakdown of the figure.The attack is the most severe in Sinai since at least July 2015, when Islamic State militants assaulted simultaneously a slew of checkpoints and military sites around North Sinai. At least 17 soldiers were killed, according to an official tally.Friday's bombings present a challenge for general-turned-president Abdel Fattah al-Sisi, who describes Islamist militancy as an existential threat and himself as a bulwark against extremism in a region beset by violence and war.