CAIRO — Egypt said its warplanes struck militant targets in North Sinai on Friday night, destroying weapons dumps as ground forces raided militant hide-outs, as part of a major offensive against the Islamic State in one of the group’s most enduring Middle East strongholds.
President Abdel Fattah-el Sisi, who is standing for re-election next month, ordered the offensive after Islamic State militants killed at least 311 people in a ruthless gun-and-bomb assault on a mosque in North Sinai on Nov. 24, in Egypt’s deadliest terrorist attack. Soon after, Mr. Sisi set a three-month deadline for the army to defeat the militants. The operation began on Friday morning.
But although the military prepared the Egyptian public for large-scale casualties, with hundreds of hospital beds set aside and doctors recalled from leave, it provided scant detail on the operation. The main news release, issued in video form by the military, featured dramatic imagery and music but no information on the scale or the goals of an operation that the military has billed as its biggest push against the Islamic State in years.
Those images — tanks firing shells, warplanes dropping bombs and armed boats sweeping through the seas — represent the kind of conventional warfare that Egypt’s American allies have actively discouraged for years. American officials have urged Egypt to adopt more low-key counterinsurgency tactics in Sinai, centered on gaining the support of local residents.
Still, the images released on Friday appeared to be mostly stock footage from previous Egyptian operations, and analysts said they were struggling to understand the specific goals of Mr. Sisi’s much-vaunted drive in Sinai.
“Egypt has announced the definitive operation against terrorism several times before, but the insurgency has only spread and become more lethal, against both civilians and soldiers,” said Michele Dunne of the Carnegie Endowment for International Peace. “It’s impossible to know if this effort will be any different.”
The operation comes days before Secretary of State Rex W. Tillerson is set to visit Cairo. For several years now, American commanders have provided intelligence assistance to Egyptian commanders in Sinai — reconnaissance imagery, intelligence gleaned from eavesdropping devices, and other information from sophisticated sensors, a military official in Washington said.
Since 2015, Egypt has also cooperated closely with Israel in Sinai, and Israeli drones, helicopters and jets have carried out dozens of attacks in the region, with Mr. Sisi’s secret approval. The Egyptian military has not said how many troops are involved in the current operation.
But the Interior Ministry said it was on maximum alert across Egypt, tightening security at power plants, places of worship and tourist sites in anticipation of possible retaliatory strikes.
While the Islamic State is crumbling elsewhere, the group has broadened its reach in Egypt in the past 15 months with suicide bombings at Christian churches in Alexandria and Cairo, and a gun attack on Christian pilgrims as they traveled by bus to a monastery in the desert south of Cairo.
The November attack on the mosque in Sinai, which spurred the operation, had targeted minority Sufi Muslims and underscored the Islamic State’s shift toward sectarian violence in Egypt.
Mr. Tillerson is scheduled to fly into Cairo as part of a five-country trip around the Middle East focused on stabilization following the defeat of Islamic State in Iraq and Syria. It will be his first visit to Egypt as secretary of state.
The Sinai operation is of utmost sensitivity to Mr. Sisi, a former general who cleared the field of serious rivals in the presidential vote scheduled for March 26-28, yet is cracking down harder than ever on critics and dissenters.
The military arrested and jailed a former army chief of staff, Sami Anan, who tried to run against Mr. Sisi in the election, while the families of two journalists who disappeared last Sunday said they believed they were being held by Egyptian security. Opposition leaders have denounced the March election as a “farce” and urged Egyptians to boycott the vote.
Sinai is out of bounds to most reporters, yet Mr. Sisi’s government has warned journalists covering the Sinai operation that they face potential prosecution if they publish unofficial casualty estimates or other unsanctioned information from the fight.