Security officials, speaking on condition of anonymity because the operation was still under way, said two army units responsible for clearing mines and one border-guard unit had joined the hunt, which entered its second week on Sunday.
The force was focused on Halal mountain, an 1800-metre peak that is full of caves and deep ravines and near the Israeli border.
The security force suffered a major blow on Thursday, when a police major general and a lieutenant colonel were killed in a land mine explosion. A mine wounded a third senior police official on Saturday during the operation, about 60km south of the Mediterranean coastal town of el-Arish.
Those killed were thought to be the highest-ranking police officers to die in a conflict since Egypt put down an insurgency in the mid-1990s.
Police have said they think some of the suspects holed up in the rugged mountain area are linked to the triple July 23 attacks in the southern Sinai resort of Sharm al-Shaikh that killed 64 people, as well as the 7 October bombings of two Egyptian resorts near the Israeli border that killed more than 30 people.
On Sunday, masked men in a vehicle opened fire at a security checkpoint near Halal, but no one was hurt. The men fled into the mountains.
Tourists pass debris of cars after
Since the sweep began, more than 700 Egyptians have been detained, with many subsequently released. It is not known whether any charges have been filed. An additional 15 people were arrested on Sunday.
Two pro-government newspapers reported on Sunday that authorities said that the mines, newly employed by the suspected militants to protect their hide-outs, were not among the uncounted buried explosives left over from past Arab-Israeli wars. Nor, the papers said, were the explosives fashioned from dynamite used in stone quarries in the region.
The papers, al-Ahram and al-Akhbar, said the explosive material in the mines was similar to that used Sharm and Taba bombings. They cited forensic reports as saying the explosives were imported.
One security official has said that a key suspect thought to have harbored suspects linked to the Taba attack – Salem Khadr el-Shenoub – was thought to be among militants hiding in the rugged area. El-Shenoub was tried in absentia for armed robbery and sentenced to life in prison. He has been on the run since the Taba attacks in October.
Sinai’s soaring, jagged mountains and vast desert plains have long been a haven for criminals, fugitives and Bedouin tribesmen involved in smuggling and drug trafficking.
Israel also complains that weapons smugglers used the region to smuggle weapons to Palestinian militants in the Gaza Strip. Egypt, which will soon take over control of a narrow corridor along the Gaza-Egypt border when Israel completes its military withdrawal, has vowed to secure the volatile area.