Hamas has named its Gaza leader Yahya Sinwar as the group’s new chief, following Ismail Haniyeh’s assassination in Iran last month.

The group confirmed the decision in a statement on Tuesday, local time.

The appointment comes as Israel and the region prepare for Iran’s “harsh retaliation” to the killing in its capital, Tehran.

“The Islamic Resistance Movement Hamas announces the selection of Commander Yahya Sinwar as the head of the political bureau of the movement, succeeding the martyr Commander Ismail Haniyeh, may Allah have mercy on him,” the movement said in a brief statement.

The news was greeted with a salvo of rockets from Gaza from the bands of militants still fighting Israeli troops in the besieged enclave.

Sinwar, the architect of the most devastating attack on Israel in decades, has been in hiding in Gaza, defying Israeli attempts to kill him since the start of the war.

He became the most powerful Hamas leader left alive following the assassination of Haniyeh.

Israel has not claimed responsibility for the assassination but said it killed other senior leaders, including Hamas deputy leader Saleh al-Arouri, who was killed in Beirut, and Mohammed Deif, the movement’s military commander.

Israel’s chief military spokesman, Rear Admiral Daniel Hagari, blamed Sinwar for the October 7 terror attacks and said Israel would continue to pursue him.

“There is only one place for Yahya Sinwar, and it is beside Mohammed Deif and the rest of the October 7th terrorists,” he told Al-Arabiya television, according to a statement released by the military.

“That is the only place we’re preparing and intending for him.”

The Australian government classes Hamas as a terrorist organisation and its actions on October 7, 2023 as a terrorist act.

Sworn enemy of Israel

Sinwar had made no secret of his desire to strike hard at Israel, the country that imprisoned him for almost half his adult life.

In December 2022, the militant leader told a rally in Gaza that the Palestinian group Hamas would deploy a “flood” of fighters and rockets against Israel, in a speech to supporters that bore the hallmarks of crowd-pleasing hyperbole.

“We will come to you, God willing, in a roaring flood. We will come to you with endless rockets, we will come to you in a limitless flood of soldiers, we will come to you with millions of our people, like the repeating tide,” he said in his address.

Less than a year later, Israel discovered it was no idle threat, when Hamas gunmen broke through Gaza’s fence on October 7, staging the terrorist attack that killed 1,200 people and took more than 250 hostages, according to Israel.

Israel has in response killed almost 40,000 Palestinians, according the Gaza health ministry, and left the densely populated enclave in ruins.

Twelve years ago, Yahya Sinwar was inside an Israeli jail cell with no means of escape. Now, Israel has accused the Hamas Gaza chief of playing a role in planning the October 7 attack.

Sinwar, 61, began his career as a ruthless enforcer who punished and killed collaborators with Israel, before rising to a leadership role after his release from prison in 2011 and his return to Gaza.

Both Hamas leaders and Israeli officials who know Sinwar agree he is devoted to the movement to an extraordinary level.

One Hamas figure based in Lebanon described him as “puritanical … with an amazing ability of endurance”.

Michael Koubi, a former Shin Bet official who interrogated Sinwar for 180 hours in prison, said he clearly stood out for his ability to intimidate and command. Mr Koubi once asked the militant, then aged 28 or 29, why he was not already married.

“He told me Hamas is my wife, Hamas is my child. Hamas for me is everything.”

Sinwar was arrested in 1988 and sentenced to consecutive life terms accused of planning the abduction and murder of two Israeli soldiers and the murder of four Palestinians.

In jail, his hard line against collaborators continued, Israelis who dealt with him have said.

At times, “he did not have Jewish blood on his hands, he had Palestinian blood on his hands,” Yuval Bitton, previously head of the Israel Prison Service’s intelligence division, told Channel 12 TV in October.

Mr Bitton said Israeli medics removed a tumour in Sinwar’s brain in 2004. “We saved his life and this is his thanks,” said Mr Bitton, referring to October 7. Mr Bitton’s nephew was killed during the attack and his body taken to Gaza by the militants.

Mr Koubi described Sinwar as being devoted to the destruction of Israel and to killing Jews. The senior Israeli official described him as a “psychopath”, adding that “I don’t think the way he grasps reality is similar to more rational and pragmatic terrorists”.

Mr Bitton added that the Hamas leader was willing to allow huge suffering for a cause and had once in prison led 1,600 prisoners to the brink of a mass hunger strike until death if needed in protest at the treatment of two men in isolation.

“He was ready to pay any price for the principle,” he said.