Hamas announced on Tuesday the appointment of Yahya Sinwar, its top official in Gaza who planned the attacks of October 7 in Israel, as its new leader in a dramatic signal of the power of the group's hardline wing after the killing of his predecessor in an alleged Israeli strike in Iran.

Sinwar's selection, a secretive figure close to Iran who has worked for years to build Hamas's military strength, is a challenge that the group is prepared to continue fighting after 10 months of devastation caused by Israel's campaign in Gaza and after the assassination of Sinwar's predecessor, Ismail Haniyeh.

This is also likely to provoke Israel, which placed him at the top of its kill list after the October 7 attack, which killed 1,200 people in southern Israel and kidnapped about 250 hostages.

The announcement comes at a volatile moment. There are significant fears of escalation to a broader regional war, with Iran pledging revenge against Israel for the killing of Haniyeh and Hezbollah threatening retaliation for the killing of one of its senior leaders in an Israeli airstrike in Beirut last week. U.S., Egyptian, and Qatari mediators are trying to salvage negotiations for a ceasefire and the release of hostages in Gaza, which has been rocked by Haniyeh's assassination.

Hamas said in a statement that it appointed Sinwar as its new political bureau chief to replace Haniyeh, who was killed in an explosion that both Iran and Hamas blamed on Israel. Israel did not confirm or deny responsibility. Last week as well, Israel said it confirmed the killing of Hamas’s military wing chief, Mohammed Deif, in an airstrike in Gaza in July. Hamas did not confirm his death.

In response to the appointment, Israeli military spokesman Rear Admiral Daniel Hagari told Saudi-owned Al Arabiya: "There is only one place for Yahya Sinwar, and that is next to Mohammed Deif and the rest of the terrorists of October 7. That is the only place we have prepared and intend for him."

Israel's killings of numerous senior Hamas officials in recent months have made Sinwar the most prominent figure in the group. His selection indicates that ground leadership in Gaza - especially the military wing known as Izz ad-Din al-Qassam Brigades - has taken charge in exile, which has traditionally maintained the top leadership position in dealing with foreign allies and diplomacy.

Haniyeh, who has been living in voluntary exile in Qatar since 2019, played a direct role in negotiating ceasefire matters in Gaza through American, Qatari, and Egyptian intermediaries - although he and other Hamas officials have always presented Sinwar's proposals and stances.

Hamas spokesman Osama Hamdan stated in an interview with Al Jazeera following the announcement that Sinwar will continue the ceasefire negotiations, saying, "The problem in the negotiations is not the change in Hamas," blaming Israel and its ally the United States for the failure to reach an agreement.

However, he said that Sinwar's selection was a sign that the group's will has not been broken. Hamas "remains steadfast on the battlefield and in politics." "The person leading today is the one who has led the fight for over 305 days and is still steadfast in the field."

Hamas allies, Iran and Hezbollah, issued statements praising Sinwar's appointment.

Hamas representative in Iran, Khaled Qaddoumi, described Sinwar as a "consensus choice" popular among all factions and constantly involved in decision-making within the group, including during negotiations. In a voice message to the Associated Press, Sinwar stated that he knows the political aspirations of Palestinians for statehood and the return of refugees, but he is also "a fierce fighter on the battlefield."

Mediators have struggled to push through a U.S.-backed plan for an agreement, but talks have faced obstacles, especially concerning its core conditions - the release of all remaining Hamas hostages in exchange for ending the war and the complete withdrawal of Israeli forces from Gaza.

Hamas demanded guarantees from the mediators that the initial ceasefire would last until terms for this exchange are reached. Israeli leaders threatened to resume fighting to eliminate Hamas after an initial partial release of hostages.

Speaking on Monday, U.S. Secretary of State Antony Blinken said: "Escalation is not in anyone's interest, and will only lead to more conflict, more violence, more insecurity, ... It is also critical that we break this cycle by reaching a ceasefire in Gaza. This in turn will open possibilities for more lasting calm, not only in Gaza itself but in other areas where the conflict could spread."

White House spokesperson Karine Jean-Pierre told reporters Tuesday at a news briefing that she had no comment on the announcement of Sinwar's appointment.

As Hamas leader inside Gaza since 2017, Sinwar has rarely appeared in public but has maintained a tight grip on Hamas’s rule over the region. As a close ally of both the Deif and Qassam Brigades, he has worked to boost the group's military capabilities.

In one of his few appearances, Sinwar ended a public speech in Gaza by inviting Israel to assassinate him, declaring, "I will go home after this meeting." He then did so, shaking hands with people and taking selfies with them in the streets.

He has been in hiding since the October 7 attacks, which sparked a campaign of bombings and Israeli strikes aimed at destroying Hamas. The Palestinian death toll is now approaching 40,000, with most of Gaza's 2.3 million residents displaced from their homes, and vast areas of Gaza's cities and towns destroyed. In May, prosecutors at the International Criminal Court sought to issue an arrest warrant for Sinwar on war crimes related to the October 7 attack, as well as against Israeli Prime Minister Benjamin Netanyahu and the Israeli defense minister on war crime charges.

Hugh Lovatt, a Middle Eastern expert at the European Council on Foreign Relations, said that the elimination of other prominent figures paved the way for Sinwar. He said: "Two weeks ago, no one expected Sinwar to be the next leader of the group despite the strong influence he wields from Gaza."

He noted that the killing of Haniyeh, a relatively moderate figure, "not only opened the way for Sinwar to claim full control of Hamas but also seems to have pushed the group in a more hardline direction."