Israelis welcomed news that a top Palestinian militant had been killed, but feared that it might impede the release of hostages and kindle a broader war.
A day after a blast killed a senior Hamas leader outside Beirut, Lebanon, many Israelis welcomed the assassination as an important step in the campaign to destroy the militant group, but worried it might carry costs.
Members of Prime Minister Benjamin Netanyahu’s right-wing coalition in Israel, in particular, cheered the attack. “All those involved in the October massacre should know we’ll get to them, and we’ll settle the score,” declared Danny Danon, a member of Parliament from the Likud party.
But some analysts said the killing of the Hamas official, Saleh al-Arouri, was likely to disrupt any negotiations over freeing more hostages taken in the Hamas-led attack on Oct. 7 — which would be another setback for Israeli families waiting desperately for their relatives to come home.
The assassination also prompted fears of a wider war in the Middle East and of retaliatory attacks in Israel.
On Wednesday, the leader of the Lebanese-based militant group Hezbollah, which like Hamas is backed by Iran, denounced the killing as a “dangerous” escalation and warned that Israel would “not go unpunished.”
“If the enemy considers waging a war against Lebanon, our battle will be without boundaries or rules,” Hassan Nasrallah, Hezbollah’s leader, said in a broadcast. “We are not afraid of war.”
In the volatile Israeli-occupied West Bank, where Mr. al-Arouri was born in 1966, there were immediate repercussions.
Palestinians went on strike there on Wednesday to protest the assassination, shutting down universities, banks, shops and other businesses. A day earlier, masked demonstrators marched in anger over Mr. al-Arouri’s death, carrying weapons and wearing headbands bearing the name of the Qassam Brigades, Hamas’s military wing, which he founded.
Israel has not taken responsibility for the explosion that killed Mr. al-Arouri and two commanders of the Qassam Brigades. Officials in Lebanon and the United States, along with Hamas, have said that Israel was behind it. Many Israelis simply took it for granted.
“So shall your enemies perish, Israel,” Bezalel Smotrich, Israel’s finance minister, wrote on social media, quoting from the Old Testament. (On Wednesday, France and Germany joined other nations, including the United States, in denouncing a call by Mr. Smotrich and another Israeli minister for Palestinians to be removed from the Gaza Strip.)
While the death of Mr. al-Arouri, a key strategist and liaison with Hamas’s Iranian sponsors, was a blow to the group, analysts said, it has rebounded from past assassinations. And the killing added to tensions along Israel’s northern border with Lebanon, where Hezbollah’s frequent rocket fire has forced communities to evacuate.
Ehud Olmert, a former Israeli prime minister, questioned the timing of the al-Arouri killing, given the war. Mr. al-Arouri’s focus, he said, had always been on the West Bank, not Gaza.
“Was he that important? I’m not so sure,” Mr. Olmert said. “There is room to ask this question: Was it urgent? Was it important to do this now? And was it more important than other things?”
Reflecting that sense of uncertainty, a columnist on Wednesday in the Israeli newspaper Yediot Ahronoth labeled the killing “a gamble.”
“Of all the possible reactions Hamas may take, the most disconcerting is with regard to the hostages,” wrote the columnist, Nahum Barnea. “The argument that the assassination will soften Sinwar’s position is just a story we tell ourselves,” he wrote, referring to Yahya Sinwar, Hamas’s leader in Gaza. Instead, he wrote, the killing is more likely to “delay, or even torpedo, the negotiations” for the hostages’ release.
Mr. Netanyahu met with representatives of hostage families on Tuesday evening, around the same time that Mr. al-Arouri was killed, and told them that efforts to free their relatives were continuing. “The contacts are being held; they have not been cut off,” he said.
But many families have been increasingly skeptical of Mr. Netanyahu’s promises to make the hostages’ return a top priority in the war. Now, they fear that the hostages could be mistreated or even killed in retaliation for the assassination.
“Of course this doesn’t help — it hurts,” said Lior Peri, whose father, Chaim, 79, was kidnapped from Nir Oz, an Israeli kibbutz close to the Gaza border. “I don’t know who’s in charge and giving the order, but they’re definitely not thinking about the hostages.”
Some Israelis who are familiar with the seemingly endless cycle of attacks and counterattacks in the Middle East were bracing for retribution.
After the assassination, Rear Adm. Daniel Hagari, the Israeli military’s chief spokesman, said Israeli forces were “on very high alert on all fronts, for defensive and offensive actions.” But in what some analysts interpreted as an indication that Israel was not seeking a wider war with Hezbollah, Admiral Hagari emphasized that it was “focused on fighting Hamas.”
Israeli public support for destroying Hamas is broad but not unqualified. After almost three months of war, there is growing international outrage over the number of Palestinian civilians being killed. And many Israelis are beginning to openly question whether the goal of destroying Hamas is realistic — and whether the cost of doing so would be bearable.
Most senior Hamas leaders within Gaza have eluded capture, and though Israel has begun pulling some troops out of the enclave in what appears to be the start of a shift toward a more targeted assault, few Israelis were prepared for a conflict of this length and with such heavy casualties.
The Israeli military said on Wednesday that one of the hostages in Gaza, Sahar Baruch, 25, was killed last month during a rescue attempt. It said that it was not yet possible to determine whether he had been killed by Hamas or by Israeli fire.
While the war in Gaza has unified many Israelis, who were in political turmoil before the Hamas attack, tensions have begun to re-emerge.
On Wednesday, the Israeli Supreme Court delayed a new law that would have made it harder for a prime minister to be deemed unfit and removed from office. The court found that the law was designed to help Mr. Netanyahu, who is on trial on corruption charges. The ruling came days after the court struck down a sweeping law that would have curbed the power of the judiciary, in another blow to Mr. Netanyahu.
Euan Ward contributed reporting from Beirut, Lebanon; and Talya Minsberg and Michael Levenson from New York.