Hamas has named Yahya Sinwar as the new head of its political bureau, elevating the hardline militant to the group’s top post after the assassination in Teheran of its previous political leader. Sinwar’s appointment was announced in a brief statement by Hamas on Tuesday that was aired on pro-Hamas Iranian state media channels. Sinwar, the Hamas military leader who is seen as the mastermind behind the 7 October attack against Israel, is believed to be hiding in the series of tunnels underneath Gaza. He is the group’s chief decision-maker in Gaza, and is believed to hold control over the estimated 120 Israeli hostages who are still in Hamas’s custody. Sinwar succeeds Ismail Haniyeh, the former Hamas political chief who was killed in a bombing attack last week that Hamas and Iranian officials blamed on Israel. The assassination came during the inauguration of Iran’s new president and has further stirred fears of a larger regional war involving Iran, which backs Hezbollah in Lebanon and Hamas in Gaza. Iran has promised to retaliate against Israel for the attack on its soil. Haniyeh was another key figure in the talks between Israel and Hamas over a ceasefire, and was seen as an intermediary between Israel and Sinwar. Haniyeh had little direct control over Hamas militants in the Gaza Strip and was seen as a relative moderate, directing Hamas’s delegations in talks mediated by Egypt, Qatar and the US aimed at a ceasefire and hostage and prisoner release deal. Sinwar is a founding member of Hamas and is seen as the group’s most powerful figure. A former head of the group’s intelligence service, Sinwar spent 23 years in Israeli prisons as he served four life sentences for attempted murder and sabotage. A former interrogator called him “1,000% committed and 1,000% violent, a very, very hard man”. Sinwar was released as part of a swap in which Israel traded 1,000 prisoners in 2011 in exchange for Gilad Shalit, an Israeli soldier who had been captured five years earlier by Hamas. Sinwar quickly returned to militancy and said he had concluded that capturing Israeli soldiers was the key to freeing prisoners from Israel. The move will further consolidate the group under Sinwar, whose elevation to the head of Hamas’s political wing will raise further doubts about the potential for any ceasefire deal to be struck in the conflict. Sinwar is believed to have launched the 7 October attack from Gaza without informing the political leadership, which was headquartered under Haniyeh in Qatar. “In electing Sinwar to head Hamas, the organisation lays to rest any differences between external and internal leaders and whatever illusions of moderation existed to reveal its true face,” wrote Aaron David Miller, a senior fellow at the Carnegie Endowment. Israel claims it killed Hamas’s military commander, Mohammed Deif, in a strike in July, among a number of assassinations of key members of Hamas’s leadership. Another top political leader, Saleh al-Arouri, was killed in January. The policy of killing top Hamas leaders, including those from the more moderate political wing, has led to rising tensions between the US president, Joe Biden, and the Israeli prime minister, Benjamin Netanyahu. Biden last week told Netanyahu during a phone call that the Israeli PM was intentionally sabotaging efforts to conclude a ceasefire, according to the New York Times and other US media. Netanyahu argued that the assassination in Teheran would temporarily delay negotiations, but would ultimately lead to a ceasefire more quickly by putting pressure on Hamas. In reaction to Sinwar’s appointment, Israeli military spokesperson Rear Adm. Daniel Hagari told Saudi-owned Al-Arabiya televsion: “There is only one place for Yahya Sinwar, and it is beside Mohammed Deif and the rest of the October 7th terrorists. That is the only place we’re preparing and intending for him.” Speaking to Al Jazeera television after the announcement, Hamas’s spokesperson Osama Hamdan said Sinwar would continue the ceasefire negotiations. “The problem in negotiations is not the change in Hamas,” he said, blaming Israel and its ally the US for the failure to seal a deal.