The Israeli military said it had killed senior Hamas commander Raed Saeed in a car strike in Gaza City, "Reuters" reports.
Saeed was one of the "architects" of the attacks on Israel on October 7, 2023.
This is the most high-profile assassination of a senior Hamas leader since the Gaza ceasefire agreement took effect in October.
In a joint statement, Israeli Prime Minister Benjamin Netanyahu and Defense Minister Israel Katz said Saeed was targeted in response to a Hamas attack in which an explosive device wounded two soldiers earlier on Saturday.
The car attack in Gaza City killed five people and wounded at least 25 others, according to Gaza health authorities. There was no immediate confirmation from Hamas or medics that Saeed was among the dead.
Hamas sources described him as the second in command of the group's armed wing, after Izeldeen al-Haddad.
Saeed led Hamas's Gaza City battalion, one of the group's largest and best-equipped, the sources said.
In a statement, Hamas condemned the attack as a violation of the ceasefire agreement, but did not say whether Saeed was injured or threaten retaliation.
The Gaza war began after Hamas-led militants killed 1,200 people, most of them civilians, and took 251 hostages in an attack on southern Israel on October 7, 2023. Israel's retaliatory offensive has killed more than 70,700 Palestinians, most of them civilians, Gaza health officials say.
The ceasefire of October 10 has allowed hundreds of thousands of Palestinians to return to the ruins of Gaza City. Israel has withdrawn its troops from positions in the city, and aid flows have increased.
But the violence has not stopped completely. Palestinian health officials say Israeli forces have killed at least 386 people in strikes in Gaza since the truce began.
Israel says three of its soldiers have been killed since the ceasefire began and that it has attacked dozens of militants.