The security situation in the arid peninsula has become increasingly precarious since the 2011 uprising.
At least 25 Egyptian soldiers have been killed in a rocket-propelled grenade attack in northern Sinai, security officials say.
The officials said the Monday morning attack took place as the soldiers were driving through a village near the border town of Rafah in the volatile Sinai Peninsula.
At least two others were injured when unknown fighters fired on the buses as the military convoy headed towards Rafah, on the border with the Palestinian Gaza Strip.
Egypt shut the Rafah crossing after the attack, an official told AFP news agency, the sole crossing into Gaza.
The bodies of the dead soldiers were later flown to a Cairo airbase.
Sinai has witnessed almost daily attacks since the July 3 overthrow of President Mohammed Morsi in a military coup.
The attack was the deadliest in the Sinai in years, exceeding the toll from an August 2012 attack on Egyptian soldiers that killed 16.
The security situation in the Sinai Peninsula, which borders both Gaza and Israel, has deteriorated since 2011, when president Hosni Mubarak was overthrown.
According to AFP news agency, at least 49 security officials have been killed in Sinai since July 5 not including those in the latest attack.
The army says it has killed nearly 70 “terrorists” in the region since July 3.
The violence comes as Egypt wrestles with a deep political crisis and bloodshed that has left hundreds of people dead in days of clashes between anti-coup protesters and security forces.