Troops and tanks backed by helicopter gunships are sweeping through villages in the northern Sinai Peninsula in a major offensive against anti-government fighters, according to an Egyptian military official.
Monday was the third day in a major operation against armed groups in the region, which has already left at least 20 people dead and 20 others detained.
The official said helicopters struck hideouts of suspected fighters early on Monday in the southern town of Rafah.
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He said that along with those killed and arrested, a number of fighters had fled to coastal villages, while others tried to enter the Palestinian territory of Gaza Strip through underground tunnels.
The air strikes took place south of the town of Sheikh Zuwayid on Sunday and near the border with the Gaza Strip on Saturday, the officials said.
Egyptian state news agency MENA said the army killed nine "terrorist elements" and arrested nine others during the operation.
The northern Sinai, which adjoins Israel and the Palestinian Gaza Strip, has long been a haven for armed groups.
The army has faced an armed anti-state campaign in the area since it toppled President Mohamed Morsi on July 3.
Several dozen soldiers and policeman have died in the violence since then, including 25 conscripts executed on a roadside after their bus came under attack.
Sources within the military told Al Jazeera that aircraft fired rockets at "terrorist hotbeds", and then soldiers on the ground went in to crack down on suspected fighters.
A witness said the column of tanks, trucks carrying infantry, rocket launchers and other military vehicles on the road on Saturday appeared to be one of the largest units deployed to the area in recent years.
The troop movement follows a failed car bomb attack on Thursday on the Interior Minister's convoy in Cairo that killed one person.
Meanwhile, also on Saturday, Egyptian military engineers defused mortar rounds rigged to explode on a railroad linking the canal cities of Ismailiya and Suez, security officials said.
Police called in the military experts after residents of a village near the railroad spotted the bomb, officials said.