White House official Jake Sullivan has said Hamas leader Marwan Issa died in an Israeli air strike.
As deputy military commander, Mr Issa would be Hamas’s most senior leader to die since the war began on 7 October.
The Palestinian group, which controls Gaza, has not officially commented on reports of his death.
Israeli media sources have reported that Mr Issa was killed in a strike on a tunnel complex under the Nuseirat refugee camp in central Gaza last week.
The deputy commander of Hamas’s military wing – the Izzedine al-Qassam Brigades, was considered one of Israel’s most wanted men.
The European Union, which placed the Hamas leader on its terrorist blacklist, linked him directly to the 7 October attack led by the group which killed approximately 1,200 people.
He had been jailed by Israel for five years during the first Palestinian intifada, or uprising, and detained by the Palestinian Authority in 1997 until the start of the second intifada in 2000.
The Israeli military has killed several Hamas’s senior leaders since 7 October. Hamas political leader Saleh al-Arouri died in an explosion in Beirut’s southern suburb of Dahiyeh. Israel is widely considered responsible for that attack.
Mr Sullivan, the White House’s national security adviser, said other Hamas leaders were believed to be in hiding, “likely deep in the Hamas tunnel network” in Gaza.
He pledged that the US would aid Israel in its continued hunt for top Hamas leaders, adding: “Justice will come for them, too.”