BEIRUT — Lebanon's Hezbollah on Friday mourned its top military commander, Mustafa Badreddine, who was killed in an explosion in Damascus, the highest level figure yet from the militant group to die since it threw itself into Syria's civil war.
Badreddine, 55, had been the mastermind of the group's involvement in Syria's civil war, which has been crucial to preserving President Bashar Assad's hold on power against rebels but which has come at a heavy cost for the Iranian-backed Shiite guerrilla force, with more than 1,000 fighters killed.
His death was a severe blow to Hezbollah, robbing it of a commander with decades of experience. But observers said the group was not likely to scale back its intervention in Syria, where it has fighters battling alongside Assad's army on multiple fronts.
"I really do think it will affect their morale. This is not just their commander in Syria. This is one of the most elite and uniquely pedigreed Hezbollah personalities," said Matthew Levitt, director of Stein Counterterrorism Program at the Washington Institute. But "I don't think they are going to waver in their commitment in this," he said, pointing to Hezbollah's own interest in stemming Sunni militants in Syria and the determination of Iran, Hezbollah's top backer, to keep Assad in power.
The cause of the explosion Thursday night that killed Badreddine remained a mystery. Hezbollah said it occurred near the Damascus airport, without giving further details.
The airport is close to the Shiite shrine of Sayyida Zeinab, where the group has strong presence and several military positions. The group said it was investigating whether the blast, which wounded several others, was from an air raid, missile attack, artillery shelling or other causes.
Hezbollah's traditional enemy, Israel, has assassinated leaders from the group in the past. But Sunni opposition forces could also be behind the explosion, including militants like the Islamic State group or al-Qaida branch in Syria, the Nusra Front. The Beirut-based Al-Mayadeen TV, which is close to Hezbollah, initially said Badreddine was killed in an Israeli airstrike but later removed the report. There was no immediate comment from Israel.
Hezbollah's deputy leader, Naim Kassem, said that by Saturday the group will release information on who was behind the killing of Badreddine.
"We will continue to confront Israel and we will continue to confront Takfiris," he told a gathering ahead of Badreddine's funeral. "Takfiris" is a term for Sunni extremists. Badreddine's body was draped with the group's yellow flag. "For us, there is only one enemy, which is Israel and those siding with it. The picture may differ and the positions may change but they are all at the end inside the Israeli project."
"By killing you, they gave a new push to our drive that produces a martyr after another, as well as a commander after another," Kassem said, addressing the slain commander.
Badreddine's death is the biggest blow to the militant group since the 2008 assassination of his predecessor and brother-in-law, Imad Mughniyeh, who was killed in a bomb attack in Damascus. After that, Badreddine became Hezbollah's top military commander and adviser to the group's leader, Sayyed Hassan Nasrallah. Badreddine was to be laid to rest next to Mughniyeh on Friday afternoon at a Shiite cemetery south of Beirut.
Badreddine's nom de guerre, Zulfiqar, was the name of double-headed sword of Imam Ali, the Prophet Muhammad's cousin and son-in-law and the Shiite sect's most sacred martyr.
Badreddine was one of four people being tried in absentia for the murder of former Lebanese Prime Minister Rafik Hariri. The 2005 suicide bombing that killed Hariri and 22 others was one of the Middle East's most dramatic political assassinations. The trial is ongoing in the Netherlands. A billionaire businessman, Hariri was Lebanon's most prominent politician after the 15-year civil war ended in 1990.
Hezbollah denies involvement in Hariri's assassination and says the charges are politically motivated.
One of the group's most shadowy figures, Badreddine was also known by aliases Elias Saab and Sami Issa. He was only known to the public by a decades-old black-and-white photograph of a smiling young man wearing a suit until Hezbollah released a new image of him in military uniform. He was suspected of involvement in the 1983 bombings of the U.S. and French embassies in Kuwait that killed five people.
The U.S. Treasury Department imposed sanctions twice on Badreddine for his involvement in the Syrian war, in 2011 and in 2015. According to U.S. officials, Assad and Nassrallah coordinated Hezbollah's actions in Syria on a weekly basis, with Badreddine present at top Damascus meetings.
Badreddine was also known for his expertise in explosives, and his trademark was to add gas to increase the power of sophisticated explosives.
In its statement announcing his death, Hezbollah said "a strong explosion targeted one of our centers near the Damascus International Airport, leading to the martyrdom of brother commander Mustafa Badreddine and wounding several others."
Top Hezbollah officials attended a mourning ceremony at a hall in southern Beirut on Friday, where Badreddine's family members received condolences. Badreddine's only son, Ali, wept as a senior Hezbollah official, Hashim Safieddine, hugged him.
Since Hezbollah was founded in 1982, Israel has killed some of the group's top leaders. In 1992, Israeli helicopter gunships ambushed the motorcade of Nasrallah's predecessor, Abbas Musawi, killing him, his wife, 5-year-old son and four bodyguards. Eight years earlier, Hezbollah leader Sheik Ragheb Harb was gunned down in south Lebanon.
In December, high profile militant Samir Kantar, who spent 30 years in an Israeli prison, was killed along with eight others in an airstrike on a residential building in Jaramana, a Damascus suburb.
Hezbollah has paid a very steep price for its public and bloody foray into Syria's civil war, beyond its casualties. Once lauded in Lebanon and the Arab world as a heroic resistance movement that stood up to Israel, its staunch support for Assad has been criticized at home, even among its Lebanese support base.
The Arab League designated Hezbollah a terrorist organization in March. A month earlier, Saudi Arabia cut $4 billion in aid to Lebanese security forces after Lebanon's Foreign Minister Gibran Bassil declined to join Arab and Islamic league resolutions critical of Iran and Hezbollah.
The predominantly Sunni Gulf Arab states, led by the kingdom, have taken other punitive measures. They have warned their citizens against traveling to Lebanon as well as cut Lebanese satellite broadcasts, and closed a Saudi-backed broadcaster in Lebanon. The Gulf countries are also expelling Lebanese expatriates they say have ties to Hezbollah.
Hezbollah, which maintains a dominant militia force in Lebanon, has also aligned itself with the Saudi-opposed Shiite Houthi rebels in Yemen's civil war.
Hezbollah's statement quoted Badreddine as saying in Syria a few months ago: "I will only return from Syria as a martyr or carrying the banner of victory."
Associated Press writer Sarah El Deeb contributed to this report from Beirut.