Egyptian President Abdul Fattah al-Sisi has cut short a visit to an African Union summit to deal with an upsurge of attacks in the Sinai peninsula.
Militants targeted military and police in North Sinai late on Thursday, which officials say killed at least 32 and wounded many more.
The group Sinai Province, which has pledged allegiance to Islamic State (IS), said it carried out the attacks.
Egypt has conducted a major security crackdown in Sinai in recent months.
Thursday's attacks represent some of the worst anti-government violence in Egypt for months, and indicate a previously unseen level of co-ordination by militants, correspondents and analysts say.
Emergency services were still digging in the rubble for bodies on Friday morning, and two children died from wounds they had reportedly received on Thursday.
Analysis: Orla Guerin, BBC News, Cairo
Sinai's most active and deadly militant group, the Sinai Province, is clearly on a learning curve. Last October, before it pledged allegiance to IS, it killed more than 30 troops in a co-ordinated attack in the peninsula.
But its latest assault was more ambitious and more sophisticated - targeting several locations simultaneously with a variety of weapons. The bloodshed is a serious challenge to President Abdul Fattah al-Sisi.
The former army chief is lauded as a military strongman, but his harsh military solutions have failed to quell the insurgency in Sinai. Some experts and many locals say the ongoing military offensive is backfiring and generating more support for Islamist militants.
With the emergence of the Sinai Province group, IS now has a foothold in another troubled corner of the Middle East - a strategic peninsula which borders the Suez Canal, the Gaza Strip and Israel. That is a concern for the region and for the US.
Most of the victims were soldiers in the provincial capital, El-Arish, where police offices, a military base and a military hotel were hit by rockets.
A car bomb exploded at the gate to the military base and several checkpoints in the city were also targeted.
Mr Sisi was returning to the Egyptian capital from an African Union summit in Ethiopia "to monitor the situation", his office said in a statement.
Sinai has become increasingly lawless since President Hosni Mubarak was overthrown in 2011, and insurgents have intensified attacks since his Islamist successor Mohammed Morsi was ousted in 2013.
Recent Sinai attacks
- Oct 2014: At least 31 soldiers killed in suicide bombing and shooting in and around El-Arish
- Sept 2014: Bomb attack near Gaza border kills at least 11 policemen
North Sinai has been under a state of emergency and a curfew since October, when an attack on a checkpoint killed dozens of soldiers.
Major military operations in the region have so far failed to quell the violence, though a military spokesman said in a Facebook post that Thursday's attacks were the result of "successful strikes" against militants.
Sinai Province, which was originally inspired by al-Qaeda, changed its name from Ansar Beit al-Maqdis when it pledged allegiance to Islamic State in November.
The group has called on Egyptians to rebel against Mr Sisi.
As part of its security crackdown in Sinai, Egypt has been creating a 1km (0.6-mile) buffer zone along the border with Gaza in a bid to stop militants smuggling weapons through tunnels from the Palestinian territory.
The project has displaced more than 1,000 families in Rafah and severed an economic lifeline for many Palestinians.
One of the targets of Thursday's attacks was a checkpoint in Rafah, where medical and security sources said an army major had been shot dead.
In a separate incident, a police officer was killed in the canal city of Suez, and officials said a suspected militant killed himself whilst trying to plant a bomb in Port Said.
The US condemned the Sinai attacks, saying it remained "steadfast in its support of the Egyptian government's efforts to combat the threat of terrorism".