The chief of Israel’s Mossad intelligence service is vowing that the agency will hunt down every Hamas member involved in the October 7 attack on Israel, no matter where they are. His pledge Wednesday came a day after the deputy head of the Palestinian Arab militant group was killed in a suspected Israeli strike in the Lebanese capital, Beirut.

Israel has refused to comment on reports it carried out the killing, but the remarks by David Barnea appear to be the strongest indication yet it was behind the blast. He made a comparison to the aftermath of the slayings at the Munich Olympics in 1972, when Mossad agents tracked down and killed Palestinian militants involved in slaying the Israeli athletes.

Israel was on high alert Wednesday for an escalation with the Iran-backed terrorist group Hezbollah after the strike in the Lebanese capital killed Saleh Arouri, the most senior Hamas terrorist slain since the war in Gaza erupted nearly three months ago. The strike in Hezbollah’s southern Beirut stronghold could cause the low-intensity fighting along the Lebanon border to boil over into all-out war.

In a speech Wednesday evening, Hezbollah’s leader, Hassan Nasrallah, promised revenge, repeating his group’s statement that “this dangerous crime” of Arouri’s killing will not go “without response and without punishment.” He left the audience guessing as to when and in what form.

Mr. Nasrallah said Hezbollah had so far been careful in its strategic calculus in the conflict, balancing “the need to support Gaza and to take into account Lebanese national interests.” If, though, the Israelis launch a war on Lebanon, the group is ready for a “fight without limits.”

“They will regret it,” he said. “It will be very, very, very costly.”

Mr. Barnea said that the Mossad is “committed to settling accounts with the murderers who raided the Gaza envelope,” referring to the area of southern Israel that Hamas attacked. He vowed to pursue everyone involved, “directly or indirectly,” including “planners and envoys.”

“It’ll take time, as it took time after the Munich massacre, but we will put our hands on them wherever they are,” he said. 

In Turkey, in the meantime, authorities stated on Tuesday that they had arrested 33 individuals who Turkey says were part of an alleged Mossad spy ring. A widespread hunt spanned eight Turkish provinces and authorities were as of Wednesday pursuing an additional 13 suspects being targeted for alleged espionage for Israel. 

Last month, President Erdogan warned Israel of a “heavy price” to pay if Hamas members were to be harmed on Turkish soil. That warning followed the publication of a recording of the head of Israel’s Shin Bet security agency stating that  Jerusalem could kill leaders of Hamas “in every location,” including “in Lebanon, in Turkey, in Qatar.”

Mr. Barnea had been speaking at the funeral of a head of Mossad, Zvi Zamir, who died at age 98 a day earlier. Mr. Zamir headed the agency at the time of the Munich attack, in which Palestinian terrorists killed 11 members of the Israeli Olympic delegation. Israel subsequently killed members of the Black September terrorist group who carried out the attack.

Hezbollah and the Israeli military have been exchanging fire almost daily over the Israeli-Lebanese border since the war in Gaza began. Yet Mr. Nasrallah has appeared reluctant to escalate it further, perhaps fearing a repeat of the monthlong war in 2006, when Israel bombed Beirut and southern Lebanon.

At the same time, Hezbollah also faces pressure to show support for its ally Hamas. Mr. Nasrallah’s comments on balancing interests reflected the group’s wariness of being blamed by Lebanese if its exchanges with Israel spiral into an all-out war that brings destruction similar to the 2006 war.

He avoided specifics on any possible reprisal for Arouri’s killing, though he said he would address the issue further in a speech Friday. But he said if Israel attacks Lebanon, it would be in the national interest to fight back. “We are not afraid of war,” he said. “If the enemy thinks about launching a war against Lebanon, then we will fight back without ceilings and without limits.”