At least 31 people were killed or injured on Saturday when the Egyptian army mounted a large operation against militants in North Sinai, security officials said.
Dozens of armored vehicles backed by attack helicopters took part in the operation near Sheikh Zuweid, a few kilometres (miles) from the Palestinian Gaza Strip.
Another 15 people were detained in the operation.
According to a military official quoted by the Ma'an news agency, the force assembled by the Egyptian army "could be the biggest in Egypt's modern history to join such domestic operation."
The official said that the army would target gunmen holed up in Rafah and Sheikh Zuweid.
Last Tuesday the Egyptian army reportedly killed 15 suspected gunmen in the Sinai Peninsula in an attack by army helicopters.
The Sinai has been a headache for Egyptian authorities as a stronghold for militants protesting the ousting of the former Egyptian president Mohamed Morsi.
Egyptian soldiers discovered explosives planted on a railway line on Saturday, the state news agency reported, another sign of an insurgency after an assassination attempt against a minister and attacks on security forces and a ship.
Mortars were among the munitions found on the line between the cities of Suez and Ismailia, MENA news agency said, adding that the explosives were defused by experts.
Train traffic on the line was suspended pending an army search of the area, state newspaper Al-Ahram said on its website, quoting an army official.
Egypt's interior minister survived an assassination attempt unscathed on Thursday when a car bomb blew up next to his convoy, which he said was the start of a likely wave of violence against the military-installed government.
Last Saturday, gunmen opened fire on a ship in the northern section of the Suez Canal. The canal chief blamed that on a "terrorist", suggesting Islamist militants could have been behind it.
A major attack on the Suez Canal would hammer Egypt's economy, which depends heavily on revenue from the 192-km (120 mile) waterway, the quickest sea route between Asia and Europe.
Egypt has faced a rising number of militant attacks on security forces in the nearby North Sinai region after the army, prompted by mass protests, ousted the country's first freely elected president, Islamist Mohamed Morsi, on July 3.
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