Egypt's President Abdel Fattah al-Sisi said a suicide bombing, by a suspected jihadist, which killed 30 soldiers in the Sinai peninsula was carried out with "external support".
Egypt imposed a state of emergency across parts of Sinai as the military pounded suspected jihadists after Friday's suicide car bombing.
The suicide attack was the deadliest on Egyptian security forces since the army deposed Islamist president Mohamed Morsi last year, to the fury of his supporters.
The state of emergency in the north and centre of the Sinai will remain in place for three months, the president's office said.
A curfew is in force from 5:00 pm to 7:00 am.
Egypt also announced it would close the Rafah crossing into the Gaza Strip, the only entry to the Palestinian territory not controlled by Israel.
Witnesses told AFP that new security checkpoints were erected in Rafah and the north Sinai town of Sheikh Zuweid.
"The army and police will take all necessary measures to tackle the dangers of terrorism and its financing, to preserve the security of the region... and protect the lives of citizens," a presidential decree said.
Despite killing or arresting many militants, the army has so far been unable to eradicate them in a massive operation involving attack helicopters and tanks.
The military launched fresh air strikes Saturday in northern Sinai, killing eight suspected militants, security officials said.
Sisi, the army chief who toppled Morsi and was later elected head of state, chaired a meeting of the Supreme Council of the Armed Forces Saturday.
After the meeting, the president said Friday's attack was carried out with "external support" in order to "break the will of the Egyptian people and army."
- 'Reinforce struggle against terrorism' -
"A committee comprising senior army officials was formed to examine the latest terrorist attacks in Sinai... in order to reinforce the struggle against terrorism," a statement said.
And the government announced a bill that would bring under the jurisdiction of military tribunals "matters of terrorism... linked to attacks on army and police installations and personnel, as well as vandalism and the blocking of roads."
The European Union and United States both denounced the latest incident, with the State Department saying "a prosperous and dynamic Egypt requires an environment of security and stability."
In a separate statement, the US defense Department a strongly condemned the suicide attack and stressed its support for "Egypt's efforts to counter the threat of terrorism."
Security officials said the 30 victims were killed when a suspected jihadist rammed his explosives-packed vehicle into a checkpoint in El-Arish, the main town in north Sinai.
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Medics said 29 others, including a senior army officer and five others, were also wounded.
On Saturday, the body of a soldier who disappeared after Friday's attack was found riddled with bullets, security officials said.
Gunmen also shot dead an officer and wounded two soldiers Friday at another checkpoint south of El-Arish, security officials said.
- Tourism hit -
Jihadists in the peninsula have killed scores of policemen and soldiers since Morsi's overthrow to avenge a bloody police crackdown on his supporters.
The violence has dealt a further blow to a tourism industry already reeling since a 2011 uprising that overthrew long-time president Hosni Mubarak.
While south Sinai is dotted with tourist resorts on the Red Sea -- a popular destination for scuba divers -- the lawless north is a base for militants who have launched a wave of attacks, mostly targeting security forces.
The peninsula's southern coastline has been largely spared the violence rocking the country since 2011, partly thanks to security checkpoints in the region.
But it has not been completely untouched by the militants.
In February, a suicide bomber killed three South Korean tourists in an attack on a bus in the south Sinai resort of Taba that was claimed by Ansar Beit al-Maqdis, the most active militant group in Egypt.
After Friday's attack, Sisi announced three days of national mourning.
It was the latest in a string of bloody attacks against security forces in Egypt.
Many have been claimed by Ansar Beit al-Maqdis, which tried last year to assassinate the interior minister in Cairo.
The group has expressed support for Islamic State (IS) group jihadists in Iraq and Syria, although it has not formally pledged its allegiance.
The latest bombing came after an Egyptian military court sentenced to death seven members of Ansar Beit al-Maqdis Tuesday for deadly attacks on the army.
Since Morsi's ouster, more than 1,400 of his supporters have been killed in a crackdown by the authorities. More than 15,000 others have been jailed, including Morsi, and over 200 sentenced to death.