Tehran added to the combustible mix by announcing that the strike — neither confirmed nor denied by Israel — also killed a senior Iranian general, underscoring the extent of Iran and Hezbollah's deep involvement in the volatile area on Israel's doorstep.
Sunday's deadly attack placed Hezbollah in a tough spot, as it weighs carefully how to respond. A significant retaliation risks drawing even tougher Israeli reprisals, plunging Lebanon into yet another crippling war with the Jewish state for which there is very little appetite among Lebanese public opinion.
Stretched thin and neck-deep in Syria's civil war where the group's Shiite fighters are battling alongside President Bashar Assad's forces, Hezbollah must also decide whether it can afford to open up another front with Israel.
Jihad Mughniyeh, who was buried Monday in south Beirut, did not hold a particularly senior rank in the party. But he was the son of Imad Mughniyeh, a top Hezbollah operative widely considered to have built Hezbollah's military operations infrastructure and the second most revered figure inside Hezbollah.
He was assassinated in 2008 in Damascus in a bombing that Hezbollah says was carried out by Israel's Mossad spy agency.
The 25-year-old Mughniyeh took on a more prominent role after the death of his father. He has been photographed with Sheikh Hassan Nasrallah, the group's leader, and with the powerful Iranian Gen. Ghasem Soleimani, highlighting his prominence within the group.
"For Hezbollah leaders, rank and file, and core supporters, the attack against Jihad Mughniyeh is akin to an attack against a member of their own family," said Randa Slim, a director at the Washington-based Middle East Institute.
"The fact that Hezbollah has not avenged Imad Mughniyeh's death to-date raises the bar for Nasrallah and Hezbollah military leadership to react in a big way this time... irrespective of the risks of an escalation," she said.
Mughniyeh, who had recently been entrusted with overseeing operations in the Golan Heights, is the group's most prominent figure to die so far in Syria since Hezbollah joined the conflict next door in 2012, fighting on Assad's side against the Sunni-led rebellion.
The airstrike exposed Hezbollah's involvement in the Golan area — which is now host to an explosive mix of al-Qaida-linked Syrian rebels, Syrian government forces, Hezbollah operatives and Israeli soldiers, all operating in close proximity.
Hezbollah's Manar television channel broadcast footage from the site of the airstrikes, showing a mangled wreck of metal amid snow; nearby the footage showed radar installations and a military base that the channel said was in Israeli-controlled territory.
Israeli officials had long expressed concern about Hezbollah activities along the border and blamed the group for a number of roadside bombings last year in the area.
In an hours-long TV interview last week, Nasrallah denied Hezbollah was involved in any "resistance work" in the Golan, claiming that the group was only offering support, assistance or training to Syrian groups there.
Eyal Ben-Reuven, a reserve Israeli general and former deputy head of its northern command, said the presence of such a high-ranking official on Israel's doorstep indicated that Hezbollah and Iran were planning something big against Israel.
Hezbollah said its fighters were targeted as they were "inspecting positions" near the Israeli-controlled border in the Golan.
Thousands of people lined the streets of the Shiite-dominated neighborhood of Ghobeiri in southern Beirut, a Hezbollah stronghold, as women threw rice and confetti from balconies to celebrate the "martyrdom" of Jihad Mughniyeh.
Hezbollah loyalists held hands as they pushed people back to make way for the funeral procession down the commercial street.
They wore badges that showed Jihad Mughniyeh with his father, and read "Jihad, Imad, Martyrdom."
"This martyrdom demands a large turnout, and those who support the resistance are prepared to give more, regardless of the loss," said a black-clad young man, who identified himself as Samer, age 25.
"They did this to terrify us," shouted a man over a loudspeaker. "But we say: death to Israel!"
"Death to Israel," the crowd roared in response.
The deaths of the six Hezbollah fighters elevated tensions between Israel and the powerful Lebanese Shiite movement, which recently boasted of rockets that can hit any part of the Jewish state. But it was also a significant setback, coming on the heels of a confirmation last week by Nasrallah that the organization had uncovered and arrested a senior operative who was spying for Israel.
In a statement published on the Iranian Revolutionary Guard's website, Tehran confirmed that an Iranian general also was killed in the Israeli airstrike.
It said Gen. Mohammad Ali Allahdadi was on assignment in Syria, giving "crucial advice" to Syrians fighting terrorists, a reference to Sunni rebels and Islamic extremists fighting against Assad's troops.
Allahdadi is not the first Iranian general to die in Syria. Iran accuses Israel of involvement in the killing of Gen. Hassan Shateri in February 2013 as he traveled from Syria to Lebanon. Shateri was also a commander in the powerful Revolutionary Guard.
Allahdadi's presence in the Golan, however, drew further attention to Iran's deep involvement in propping up Assad and is bound to unsettle Israel.
Although he did not mention Lebanon or Syria specifically, Israeli Prime Minister Benjamin Netanyahu said Monday that "Israel is adamant that it will have the right to defend itself against all those who wish to propagate terror and other attacks against its citizens, against its territory."
Since Syria's conflict began in March 2011, Israel has carried out several airstrikes in Syria that have targeted sophisticated weapons systems, including Russian-made anti-aircraft missiles and Iranian-made missiles, believed to be destined for Hezbollah.
The last such airstrike was in early December, when Israeli warplanes struck near Damascus' international airport, as well as outside a town close to the Syria-Lebanon border.
Nasrallah, in an interview last week, said Hezbollah reserves the right to retaliate for those attacks. He also reiterated that Hezbollah may retaliate at any time for the assassination of Mughniyeh senior.
Also among those killed in Sunday's attack was Mohammad Issa, the only one of the six identified by the Hezbollah statement as a commander. He joined Hezbollah at the age of 15 and was among the senior cadres who headed the group's operations in Syria.
Another is Abbas Hijazi, whose father Kamal was one of Hezbollah's founders. Hijazi took part in most of Hezbollah's battles against Israel as well as inside Syria over the past decade.
Associated Press writers Nasser Karimi in Tehran, Bassem Mroue in Beirut, Ian Deitch and Aron Heller in Jerusalem contributed to this report.
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