The Israeli military said on Thursday it had killed Muhammad Deif, the Hamas commander who is believed to have been a planner of the Oct. 7 attack on Israel, in an airstrike last month, which would make him the third Iranian-backed militant leader slain in recent weeks.

The Israeli announcement confirming the death of Mr. Deif, the leader of Hamas’s military wing, came as thousands of mourners attended the funerals of another Hamas leader and a Hezbollah commander whose assassinations this week have amplified fears of a wider regional war.

Mr. Deif was killed in an Israeli airstrike on a compound in southern Gaza on July 13, according to the Israeli military. It said his death had been confirmed by an intelligence assessment, but did not provide further details. At least 90 other people were killed in the strike, according to Gaza’s health officials.

Hamas has not confirmed or denied Mr. Deif’s death. The No. 2 Hamas leader in Gaza, he would be the group’s most senior military leader slain by Israeli forces during the offensive in Gaza that has also killed more than 38,000 people, according to the territory’s health officials. Israel began its campaign in the enclave after a Hamas-led attack on southern Israel on Oct. 7, during which 1,200 people were killed and about 250 abducted to Gaza.

Israeli leaders, who have said they will continue fighting in Gaza until they destroy Hamas’s military and governing capabilities, celebrated the announcement of Mr. Deif’s death, the latest revelation in a dizzying two days that have shaken the leadership of Hamas and Hezbollah, both of which are backed by Iran.