Two vehicles were blown up while passing through two checkpoints close to each other on a road outside the border city of Rafah, the sources said. No group claimed responsibility for the attacks.
The army said in a statement later on Friday the attacks had killed and injured a total of 26 soldiers, but did not provide a breakdown of the figure. It said security forces had killed 40 militants and destroyed six of their vehicles following the attack.
"Law enforcement forces in northern Sinai succeeded in thwarting a terrorist attack on some checkpoints south of Rafah," the statement said.
Egypt faces an Islamist insurgency led by Islamic State in the rugged and thinly populated northern Sinai, where hundreds of soldiers and police have been killed since 2013, when the military ousted Islamist president Mohamed Mursi after mass protests.