CAIRO — Egypt’s military said Thursday that the leader of the Islamic State’s affiliate has been killed in the Sinai Peninsula, along with several key aides and 45 other members of the extremist group.

Few details were immediately available and there was no word from the extremists’ branch in Egypt on what, if confirmed, would be a major setback for the Sinai-based militant group.

A posting on the Facebook page of the Egyptian military’s chief spokesman, Brigadier General Mohammed Samir, said Abu Doaa al-Ansari was killed in an operation south of the coastal city of el-Arish. It said the operation was carried out by counterterrorism forces backed by warplanes and guided by ‘‘accurate intelligence.’’

The statement did not provide a total number of those killed or say when the operation took place, but military officials with first-hand knowledge of the conflict in the turbulent northern part of Sinai said Ansari and his aides were killed in an airstrike.

The officials spoke on condition of anonymity because they were not authorized to discuss the operation with the media.

The name of Abu Doaa al-Ansari is not widely known and had not been previously mentioned as that of the leader of the Sunni militant group, which was known as Ansar Beit al-Maqdis, or Soldiers of Jerusalem, before it swore allegiance to the Islamic State group fighting in Syria and Iraq.

Ansari is also likely a nom de guerre, as are most names taken by those who join extremist groups. Such names often allude to the country or city a militant hails from or the place he adopted as his home.

According to the Egyptian military officials, the airstrike was part of an ongoing, intense air campaign that began more than a week ago.

The airstrikes, at least in part, were in response to the growing threat to ground troops posed by roadside bombs planted by the militants, they said.

Associated Press