Hamas leader Marwan Issa died in an Israeli air strike, White House official Jake Sullivan has said.
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 a number of 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.”
But he also emphasised that US President Joe Biden had expressed his growing alarm over the rising number of civilian deaths in Gaza in a call with Israeli Prime Minister Benjamin Netanyahu – their first conversation in a month.
The US president reiterated his commitment to Israel and its “right to go after Hamas”, according to Mr Sullivan, but he also said that it would be a “mistake” for Israel’s military to invade Rafah – a city in southern Gaza where an estimated million refugees have fled to during the war.
The invasion “would lead to more innocent civilian deaths, worsen the already dire humanitarian crisis, deepen the anarchy in Gaza and further isolate Israel internationally”, the US national security adviser told reporters.
More than 31,000 Palestinian civilians have died since the war started on 7 October, according to the Hamas-led health ministry in Gaza. The death toll has drawn international condemnation and alienated many of Israel’s allies.
President Biden pushed Mr Netanyahu for a “clear, strategic end game” in Gaza during the call, Mr Sullivan said.
The relationship between President Joe Biden and Israeli Prime Minister Benjamin Netanyahu has grown tense as the war in Gaza continues.
“The president told the prime minister again today that we share the goal of defeating Hamas, but we just believe you need a coherent and sustainable strategy to make that happen,” he said.
Mr Biden was able to get the Israeli leader to agree to sending a “senior interagency team composed of military, intelligence and humanitarian officials” to Washington in the coming days to discuss US concerns over an invasion of Rafah.
The expectation is that Israel will delay its assault until that meeting is held, Mr Sullivan said.
Mr Netanyahu confirmed the call on X, formerly Twitter, and said the two had “discussed the latest developments in the war” as well as Israel’s goals in the conflict.
The Israeli prime minister said those objectives included: “Eliminating Hamas, freeing all of our hostages and ensuring that Gaza never gain constitutes a threat to Israel – while providing the necessary humanitarian aid that will assist in achieving these goals.”
Senior Democrats in the US are growing more vocally critical of Mr Netanyahu.
On Thursday, Chuck Schumer – the top Democrat in the Senate – called for new elections in Israel, saying that Mr Netanyahu was prioritising his “political survival” over the country’s needs.
Mr Netanyahu’s Likud party pushed back, saying Israel was not a “banana republic” and that the prime minister’s policies were “supported by a large majority”.
Mr Biden told reporters in the Oval Office on Friday that he knew Mr Schumer’s remarks were coming. The president said, however, that the Senate leader had “expressed serious concern shared not only by him, but many Americans”.
(BBC)