At least 25 people, including civilians, have been killed in a spate of attacks by militants on more than a dozen army and police targets in the restive Sinai Peninsula.
The simultaneous attacks involved a car bomb and mortar rounds,officials said.
An Islamic State affiliate previously known as Ansar Beit al-Maqdis has launched several attacks against the police and the army in Sinai in recent years, particularly following the military overthrow of Islamist president Mohammed Morsi in 2013.
But the wide-ranging attacks today, which struck the Northern Sinai provincial capital el-Arish, the nearby town of Sheik Zuwayid and the town of Rafah bordering Gaza, indicate a previously unseen level of co-ordination.
The officials said today's attacks included at least one car bomb set off outside a military base and mortar rounds fired at a hotel, a police club and more than a dozen checkpoints. At least 36 people were injured, according to medical officials, who also confirmed the death toll.
Officials said the death toll is expected to rise after the military base hit by the car bomb was also struck by mortars that destroyed buildings inside the camp, burying people under the rubble.
The state news agency Mena said more than one car bomb was used in the attacks, without elaborating.
The explosions smashed windows and shook residential areas in el-Arish.
The areas where the attacks took place have been under a state of emergency and a curfew since October, when militants killed dozens of soldiers in a deadly attack on a checkpoint in Sinai.
In an attempt to stop weapons smuggling to and from the Gaza Strip, authorities demolished houses and residential buildings located within 500m of the border, where a complex network of tunnels had long been used to bring consumer goods, as well as weapons and fighters, to and from the Palestinian territory.
Ansar Beit al-Maqdis was initially inspired by al Qaida, but last year it pledged allegiance to Islamic State, which controls large parts of Syria and Iraq.
Sinai-based militants have exploited long-held grievances in the impoverished north of the peninsula, where the mainly Bedouin population has complained of neglect by Cairo authorities and where few have benefited from the famed tourist resorts in the more peaceful southern part of Sinai. The police in northern Sinai largely fled during the 2011 uprising that toppled long-time autocrat Hosni Mubarak, as militants attacked their stations and killed scores of security forces.
Egypt has a long history of Islamic militancy. Former president Anwar Sadat was assassinated by Islamic militants in 1981, and extremists carried out a wave of attacks targeting security forces, Christians and Western tourists during the 1990s.