The man believed to be the mastermind behind the October 7 massacre of Israeli citizens which claimed the lives of more than 1100 people, has been named as the new leader of Hamas. Yahya Sinwar, 61, was named as the group's political leader, while believed to be living in tunnels underneath Gaza.

His appointment as the head of the terror organisation follows the shock assassination of the previous Hamas Leader, Ismail Haniyeh, in Tehran last week. The attack, which took place inside an Islamic Revolutionary Guards Corps (IRGC) compound, is widely believed to have been carried out by Israel.

Sinwar has long been a key decision maker in Gaza, leading Hamas in the strip since 2017 - six years after getting out of prison for orchestrating the murder of two Israeli soldiers and four Palestinian collaborators in 1989. He is linked to the Al Qassam brigades that poured over the Gaza security fence in October, wiping out kibbutz and taking 250 people hostage.

News of the October 7 mastermind's appointment was first released on pro-Hamas Iranian TV channels. While at the same time, Iran's leaders look set to take revenge on Israel imminently for the political assassination in their capital, with US warships and planes on standby as tensions in the Middle East continue to ratchet up.

“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 [God] have mercy on him,” the group said in their TV address.

Yahya Sinwar is one of the few surviving founders of Hamas and has been among its most powerful figures since his release in a prison swap for a captured Israeli soldier in 2011. The Guardian reports that a former interrogator called him “1,000 per cent committed and 1,000 per cent violent, a very, very hard man”.

The selection of Sinwar, a figure Israel's Defense Minister Yoav Gallant has already sworn to "find and eliminate" for the atrocities of October 7, marks a further radical shift for the group and is likely to make further ceasefire talks difficult.

But with Hamas' former leader and key negotiator Haniyeh dead from an Israeli-linked explosion, neither side looks any closer to ending the conflict - which has now seen an estimated 40,000 Palestinian deaths.

The heightened military tensions in the Middle East reflect growing difficulties in US President Joe Biden and Israel Prime Minister Benjamin Netanyahu, as America's key ally carried out a number of assassinations on political targets across the region - taking out Milad Bidi, a member of Iran's IRGC, as well as a senior Hebollah commander in Beirut, and Hamas' Haniyeh.

Lebanese Hezbollah welcomed the appointment of Sinwar as the new political leader of Hamas. The group said in a statement: "Selecting the brother Yahya Sinwar from the heart of the besieged Gaza Strip – who is present the frontlines with resistance fighters and between the children of his people, under the rubble, blockade, killings and starvation – reasserts that the goals the enemy is seeking by killing leaders have failed."