Hamas on Tuesday appointed Yahya Sinwar as the leader of its political wing following the assassination of its former political chief, Ismail Haniyeh.

This makes Sinwar — a man known for his ruthlessness who is widely seen as having masterminded the Oct. 7 attack — the most powerful person in the organization and its face in international diplomacy.

“The most extreme part of Hamas carried out October 7 … and is now officially in power,” Michael Horowitz, a geopolitical analyst and head of intel at risk management firm Le Beck International, wrote in a post on X.

The Middle East has been on edge following the killing of Haniyeh in Iran on July 31, which Iran and Hamas blamed on Israel. Israel has stayed silent on the matter, while Iran has pledged to carry out some form of retaliatory attack on the Jewish state.

Meanwhile, Haniyeh’s killing has resulted in a much more extreme leader for Hamas, likely setting the Palestinian militant group in a direction that bodes poorly for ceasefire talks aimed at ending the war and freeing the Israeli hostages still captive in Gaza.

Haniyeh, based in Qatar, was Hamas’ lead negotiator in the cease-fire talks with Israel and was described as being more pragmatic and supportive of a deal. While the negotiations have been ongoing for months with no success, Sinwar — who is based inside Gaza and is said to have the last word on Hamas’ major decisions — often stalls or cuts off communications during the talks.

“Sinwar’s nomination for Hamas’ top job – despite his being based in Gaza – prefaces a significant hardening of the movement’s stance, particularly with regard to cease-fire talks,” Victor Tricaud, a senior analyst at consulting firm Control Risks, told CNBC.

The Palestinian leader “already had a very significant say in negotiations with Israel, but the difference now is that there will not be the comparatively pragmatic voice of Ismail Haniyeh to balance Sinwar’s uncompromising maximalist views.”

Still, his nomination is unlikely to change the dynamics of the ground war in Gaza, as killing him remains a top priority for Israel, Tricaud said. But it does deal a blow to the efforts to achieve a lasting halt in fighting and regional de-escalation; the analyst expects “heightened instability in the region to persist for several more months.”

The International Criminal Court in May said it was filing arrest warrant applications for Sinwar and Haniyeh for war crimes and crimes against humanity. It simultaneously filed arrest warrant applications for war crimes and crimes against humanity for Israeli Prime Minister Benjamin Netanyahu and his Defense Minister Yoav Gallant.

Sinwar’s elevation to Hamas’ highest position and the consequent merging of its political and military wings also complicates any potential plans for a “day after” in Gaza, for which Israel’s government has not presented a plan.

The selection will likely “incapacitate [Hamas’] legitimacy on the international stage,” Avi Melamed, a former Israeli intelligence official and regional analyst, said in an emailed note.

“In many ways, the separation of a military and political branch allowed space for Hamas to attempt to negotiate a better hostage settlement for itself with Israel and to secure its future after the current war in a future Palestinian government,” he said. “This move would challenge that tactic.”

A top target of Israel’s military, Sinwar has survived assassination attempts over the years and is believed to have spent much of the current war hiding in Gaza’s intricate network of tunnels.

This makes Hamas’ decision to appoint Sinwar as its head risky, said Ghanem Nuseibeh, who described the group as “clearly taking a gamble with an invisible leader.”

“But even worse for Israel and the mediators,” Nuseibeh, chairman of the London-based Muslims Against Antisemitism and a regional commentator, said. “Good luck negotiating with the most extreme part of Hamas who is also invisible.”