The Israeli military said it had killed Hamas leader Yahya Sinwar in an operation in the southern Gaza Strip.
"After completing the process of identifying the body, it can be confirmed that Yahya Sinwar was eliminated," it said.
There was no immediate comment from Hamas.
In Israel, families of hostages held by Hamas in Gaza said they hoped that a ceasefire could now be reached that would bring home the captives. In Gaza, pounded relentlessly by Israeli forces for a year, residents said they believed the war would go on.
Israeli Foreign Minister Katz called Sinwar a "mass murderer who was responsible for the massacre and atrocities of October 7" - the Hamas-led attack on Israel that triggered the Gaza war.
Sinwar, who was named as Hamas' overall leader following the assassination of political chief Ismail Haniyeh in Tehran in July, was believed to have been hiding in the warren of tunnels Hamas has built under Gaza over the past two decades.
His death could dial up hostilities in the Middle East where the prospect of an even wider conflict has grown. Israel has launched a ground campaign in Lebanon over the past month and is now planning a response to an October 1 missile attack carried out by Iran, ally of Hamas and Lebanon's Hezbollah.
Israel's Army Radio said the killing had occurred during a ground operation in the city of Rafah in the southern Gaza Strip during which Israeli troops killed three militants and took their bodies.
The corpse was taken away for DNA tests and checking of dental records - Israel has samples of Sinwar's DNA from time he spent in an Israeli jail.
Israel has killed several commanders of Hamas in Gaza as well as senior figures of Hezbollah in Lebanon, dealing heavy blows to its arch-foes.
Sinwar's killing raises new questions about the fate of the hostages still in Hamas' captivity, not least as Sinwar was involved in negotiations that could have led to their release.

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