BEIRUT (AP) — A Lebanese man convicted of one of the most notorious attacks in Israel’s history and who spent nearly three decades in an Israeli prison has been killed by an Israeli airstrike near the Syrian capital, the Lebanese Shiite Hezbollah group said Sunday.

Hezbollah officials have pledged to avenge the killing of Samir Kantar, sparking fears of escalation in an already volatile region. In a possible first response, three rockets were fired into Israel from Lebanon late Sunday.

Kantar had said that he had been working, with the backing of Hezbollah, to set up “the Syrian resistance” to liberate the Golan Heights, which Israel captured from Syria in 1967 and annexed 14 years later.

Hezbollah said Kantar was killed along with eight others in an airstrike in Jaramana, a suburb of the Syrian capital Damascus, on Saturday night. According to Hezbollah’s Al-Manar TV, two Israeli warplanes entered Syrian airspace and fired four long-range missiles at the residential building in Jaramana. It aired footage of what it said was the building, which appeared to be destroyed. Kantar’s brother, Bassam, confirmed his “martyrdom” in a Facebook post on Sunday.

In Lebanon Kantar is known as “the dean of Lebanese prisoners,” a reference to his long jail sentence.

In Israel, he gained notoriety for the kidnapping and grisly killing of a man named Danny Haran and his 4-year-old daughter, in the coastal town of Nahariya. Kantar was 16 at the time, and a member of the Palestinian militant group the Palestine Liberation Front.

He also killed a policeman during the attack, and is alleged to have beaten the four-year-old to death with a rifle butt. As the attack unfolded, the girl’s mother hid inside a crawl space inside their home and accidentally smothered their crying two-year-old daughter, fearing Kantar would find them.

Kantar was imprisoned in 1979 in Israel and sentenced to three life terms, but was released as part of a prisoner swap with Hezbollah in 2008. While many in Israel were outraged at his release, in Lebanon he received a hero’s welcome and the following year he was awarded Syria’s highest medal by Syrian President Bashar Assad.

Israel and Hezbollah are bitter enemies. The two countries battled to a stalemate during a monthlong war in 2006 during which Hezbollah fired thousands of rockets into Israel and Israel’s air force destroyed wide areas in Lebanon. Since then, Israeli military officials say Hezbollah has upgraded its capabilities and now possesses tens of thousands of rockets and missiles capable of striking anywhere in the country.

Many Israeli officials believe Hezbollah is currently in no position to open a new front with Israel, as it is bogged down aiding its close ally, President Assad, in the Syrian civil war.

Nevertheless, Hezbollah legislator Ali Ammar vowed to avenge Kantar’s killing, saying the militant group will not allow his blood to go “betrayed.” Ammar said the group’s military arm would determine the timing and methods chosen “to punish the killers, specifically the Israeli enemy.”

In January, the Lebanese group accused Israel of carrying out an airstrike on the Syrian side of the Golan Heights, which killed several Hezbollah members and a prominent Iranian general. Around ten days later, Hezbollah militants fired a salvo of missiles at an Israeli military convoy in a disputed border area, killing two soldiers and triggering deadly clashes that marked the most serious escalation since the 2006 war.

Gil Rabinovich, the former head of the Israeli military intelligence’s counterterrorism unit, said it was impossible to predict how Hezbollah would respond, in part because Israel has not claimed responsibility for Kantar’s killing. He noted however that Kantar was not a member of Hezbollah’s “inner circle,” reducing the probability that the group would open a new front against Israel.

“He’s important, but not so important to endanger them in a situation where they might be in direct conflict with Israel,” Rabinovich said.

Israel has previously said it would engage in the Syria conflict for two reasons only: to stop the transfer of game-changing weapons to Hezbollah in Lebanon and to disrupt preparations for attacks on Israel. The country is believed to have intercepted and destroyed a number of arms shipments headed toward the militant group and Israeli warplanes have struck targets inside Syria several times during the country’s nearly five-year conflict, although it has rarely confirmed its involvement.

Retired Israeli Maj.-Gen. Yaakov Amidror, former National Security Adviser and a Senior Fellow at the Begin-Sadat Center for Strategic Studies said that Kantar was seen as “a pivot in the efforts of Hezbollah to prepare the Golan Heights for another front against Israel.”

Israeli Cabinet minister Yuval Steinitz said he was not sorry about Kantar’s death but could not comment on the accusations that Israel was behind the killing. It is not unusual for Israel to decline to comment on such operations.

Kantar’s killing would mark the first Israeli assassination of a senior figure inside Syria since Russia launched its military operations in Syria on Sept. 30 in support of President Bashar Assad.

Israel and Russia have set up a communications channel to make sure their air forces do not clash with each other, though it was not known whether the alleged Israeli strike on Kantar had been announced to the Russians ahead of time. The Russian Defense Ministry declined comment.

An Israeli military official, speaking on condition of anonymity under briefing guidelines, said Hezbollah has a limited presence on the Syrian side of the Golan Heights, and its efforts there have been focused primarily on aiding Assad’s forces against the advances of various rebel groups. He noted, however, that several attacks along the Israeli-Syrian frontier in the Golan in recent years were believed to have been carried out by Hezbollah or its allies.

On Sunday evening, Lebanese security officials speaking on condition of anonymity in line with regulations, said militants fired three rockets into northern Israel. No one claimed responsibility for the rocket attacks.

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Associated Press writers Aron Heller in Jerusalem, Zeina Karam in Beirut, Albert Aji in Damascus, Syria and Jim Heintz in Moscow contributed to this report.

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This story has been corrected to show that the Lebanese militant group accused Israel of killing Hezbollah commanders in Golan Heights in January 2015, not January 2014.