Iran’s Revolutionary Guards confirmed the death of Haniyeh, hours after he attended a swearing in ceremony for the country s new president, and said it was investigating.

There was no immediate comment from Israeli authorities. The White House did not immediately respond to a request for comment on Haniyeh.

The news, which came less than 24 hours after Israel claimed to have killed the Hezbollah commander it said was behind a deadly strike in the Israeli-occupied Golan Heights, appears to set back chances of any imminent ceasefire agreement in Gaza.

Also read: Reaction to killing of Hamas chief Ismail Haniyeh

"This assassination by the Israeli occupation of Brother Haniyeh is a grave escalation that aims to break the will of Hamas," senior Hamas official Sami Abu Zuhri told Reuters.

He said Hamas would continue the path it was following, adding: "We are confident of victory."

Haniyeh, normally based in Qatar, has been the face of the Palestinian group’s international diplomacy as the war set off by the Hamas-led attack on Israel on Oct. 7 has raged in Gaza, where three of his sons were killed in an Israeli airstrike.

Haniyeh was seen by many diplomats as a moderate compared to the more hardline members of the Iran-backed group inside Gaza.

Appointed to the Hamas top job in 2017, Haniyeh moved between Turkey and Qatar’s capital Doha, escaping the travel curbs of the blockaded Gaza Strip and enabling him to act as a negotiator in ceasefire talks or to talk to Hamas’ ally Iran.

"All the agreements of normalisation that you (Arab states) signed with (Israel) will not end this conflict," Haniyeh declared on Qatar-based Al Jazeera television shortly after Hamas fighters launched the Oct. 7 raid which killed 1,200 people in Israel, according to Israeli tallies, and took another 250 or so to hold as hostages in Gaza, one of the most crowded places on earth.

Israel’s response to the strike has been a military campaign that has killed more than 39,000 people inside Gaza so far.