Ten Egyptian soldiers have been killed and 35 wounded in a car bomb attack near the North Sinai city of El-Arish.
Militants have stepped up assaults in the region following the army's ousting of Islamist president Mohammed Mursi in July.
The soldiers were traveling in a convoy on the road to the Rafah border crossing with Gaza.
There was no immediate claim of responsibility.
A Sinai-based militant group, Ansar Bayt al-Maqdis, said it assassinated a high-ranking security officer in Cairo on Sunday, according to a statement posted on a militant Islamist website.
That group has also said it was behind a failed suicide attack on Egypt's interior minister in September.
In a separate incident, three people were wounded in a bomb attack on a security checkpoint in Cairo, state television reported.