An attack on an Egyptian military checkpoint killed 12 soldiers and wounded six others on Friday in the Sinai Peninsula where security forces are fighting jihadists, the army said.
The Islamic State group claimed responsibility for the attack.
Mortar rounds and rockets were fired at the army post, a police official and a medic told AFP.
The army spokesman said in a statement that soldiers clashed with the assailants in the northern Sinai.
"Terrorist elements attacked a checkpoint in the northern Sinai. The clashes left 12 soldiers dead and wounded six others," the statement said.
It said that "15 terrorists were killed".
But the jihadist IS group, in a statement on the smartphone app Telegram, said its "soldiers" were "safe and sound" and had seized arms and ammunitions during the attack on the military checkpoint.
The attack took place in the Bir al-Abd area west of El-Arish, the provincial capital of North Sinai, the officials said.
The Egyptian affiliate of IS has claimed several attacks on security forces and foreigners in the Sinai in the past.
Bir al-Abd has so far been largely spared the violence that has rocked northern Sinai over the past three years.
Jihadists in Egypt have killed hundreds of soldiers and police since the military overthrew Islamist president Mohamed Morsi in 2013.
They pledged allegiance to IS more than a year later, and their attacks have persisted despite a sweeping military campaign in the peninsula which borders Israel and the Gaza Strip.
Earlier this month, gunmen killed five Egyptian police conscripts in El-Arish.
The jihadists claimed the bombing last year of a Russian airliner carrying tourists home from a Sinai resort. All 224 people on board were killed.