The campaign, which involves the army, navy, air force, border patrol and police, takes place ahead of a March election in which Egyptian President Abdel Fattah el Sisi is seeking a second term which he is widely expected to win.
Egypt began a major assault against militants on Friday focused on the Sinai peninsula, where Daesh attacks have killed soldiers, police and civilians, aiming to crush their insurgency by an end of February deadline set by President Abdel Fattah al Sisi.
The former general on November 29 ordered the military to defeat militants in North Sinai within three months, after an attack on a mosque which killed some 300 people, the deadliest such incident in the Arab world's most populous country.
Residents said they saw warplanes flying above the Suez Canal city of Ismailia, which borders North Sinai to the west. To the northeast of the vast, remote desert region, people in the Gaza Strip said they heard explosions coming from Egyptian territory.
A military spokesman said the operation would cover large parts of Sinai, but also parts of the Nile Delta and the Western Desert, where other militants have waged attacks, some believed to be staged out of neighbouring Libya.
TRT World's Joseph Hayat has more details.
The campaign, which involves the army, navy, air force, border patrol and police, takes place ahead of a March election in which Sisi is seeking a second term which he is widely expected to win.
Sisi posted on his Facebook account on Friday: "I follow with pride the heroic actions of my sons in the armed forces and police to clear Egypt's territory of terrorist elements."
Security sources said on Thursday that the operation, which had been in planning for some time, was unprecedented in its scope, coordination and size, involving thousands of troops, but did not provide further details.
"The armed forces calls upon the Egyptian people in all parts of the country to closely cooperate with law enforcement forces to confront terrorism, uproot it and immediately report any elements threatening the security and stability of the country," military spokesman, Colonel Tamer al Rifai, said in a televised address.
Rifai said in a second statement the air force had targeted militant hide-outs in north and central Sinai, while the navy tightened its maritime control to cut off supply lines.
A security source told Reuters on Thursday that security measures had been tightened with increased patrols in North Sinai province's capital al Arish and checks of residents.
According to residents, some schools in al Arish held emergency evacuation drills on Thursday.
Countdown for election
Egypt's 2018 presidential election will be held on March 26-28. The three-month deadline Sisi gave the military would expire at the end of February.
The success or failure of the military's latest push will most likely not affect the result of the election. Sisi faces only a single, last-minute challenger who has said he supports the incumbent.
All opposition figures thought to pose a serious challenge to Sisi have pulled out of the race, accusing the government of underhand tactics to ensure Sisi an easy win. Sisi says there is equal opportunity for all candidates and that the election will be free and transparent
Egypt's military has struggled to put down the Daesh insurgency in Sinai since the group set up a branch there in 2014. Daesh attacks against the army and police in Sinai had begun to escalate the previous year, and have killed hundreds of soldiers and policemen.
Sisi led the military overthrow of former president Mohamed Mursi in 2013, and was elected in a landslide vote the following year.
Sisi's critics say support for the former military commander has eroded because of tough economic reforms and a crackdown on dissidents.
His supporters say such measures are necessary to ensure stability in a country which was rocked by unrest following a 2011 uprising that toppled former leader Hosni Mubarak.