"This assassination ... takes the war to new levels and will have enormous consequences for the entire region," the Ezzedine al-Qassam Brigades, whose fighters are engaged in fierce battles with Israeli troops in Gaza, said in a statement.

Sami Abu Zuhri, a spokesperson for Hamas, said that the killing of Haniyeh, won't impact Hamas, saying that Israel won’t achieve its goals including eradicating the Palestinians.

“The occupation will not succeed in achieving its goals,” he told The Associated Press, adding that Hamas emerged stronger after past crises and the assassination of its leaders.

Abu Zuhri accused Israel of “spreading chaos and evil” in the region. He called for regional governments to speak out against Israel’s acts, and abandon “the state of silence, because more silence means more chaos.

Ceasefire uncertainty
 

Qatar's Prime Minister Sheikh Mohammed bin Abdulrahman Al-Thani on Wednesday cast doubt over the success of future mediation between Israel and Hamas following the killing of Haniyeh in Tehran.

"Political assassinations & continued targeting of civilians in Gaza, while talks continue, leads us to ask, how can mediation succeed when one party assassinates the negotiator on the other side? Peace needs serious partners," Sheikh Mohammed, who has led Qatar's mediation efforts, wrote on X.

Qatar, which hosts Hamas's political leadership that included Haniyeh, has been involved in months of back-and-forth talks to mediate an end to the war in Gaza, alongside Egypt with US support.

Earlier on Wednesday, Qatar's foreign ministry condemned the Hamas political chief's assassination, describing it as a "heinous crime" and "dangerous escalation", adding that it was "a flagrant violation of international and humanitarian law".

The foreign ministry said, "This assassination and the reckless Israeli behaviour of continuously targeting civilians in Gaza will lead to the region slipping into chaos and undermine the chances of peace".

"The ministry reiterates the State of Qatar's firm position rejecting violence, terrorism and criminal acts, including political assassinations, regardless of the motives and reasons," it added.

Qatar has hosted Hamas's political bureau with the blessing of the United States since 2012 following the Palestinian group's closure of its office in Damascus.

There was no immediate reaction from the White House to the assassination of Haniyeh.

Asked by reporters in Manila about the Tehran strike, U.S. Secretary of Defense Lloyd Austin said he had no “additional information to provide.” But he expressed hope for a diplomatic solution on the Israeli-Lebanon border.

“I don’t think that war is inevitable,” he said. “I maintain that. I think there’s always room and opportunity for diplomacy, and I’d like to see parties pursue those opportunities.”