A top Hizballah military commander has been killed in an explosion in Syria, dealing a blow to the Lebanese Shi'ite militant group and its support for the Syrian government.

Hizballah sources have blamed the death of Mustafa Badreddine in an explosion near Damascus airport on an Israeli air strike, although a deputy leader was later quoted as saying the group would announce its findings "within hours."

The Israeli Foreign Ministry has declined to comment on whether it was involved in Badreddine's death. But its forces have carried out targeted assassinations against Hizballah in the past.

Badreddine has been a key figure in the military activities of Hizballah, a sworn enemy of Israel whose military arm has sent thousands of fighters to Syria to help Russia and Iran prop up Syrian President Bashar al-Assad against internal and external enemies.

"There is no question that Hizballah lost a very important commander, the Iranians lost a very important interloper, and the Assad regime lost a great supporter," Yaakov Amidror, who was national security adviser to Israeli Prime Minister Benjamin Netanyahu from 2011-13, said of Badreddine's death. Amidror said it would have a deep impact in Syria.

Turkey and the United States have led efforts to put pressure on Assad to step down since his regime responded brutally to antigovernment unrest that began early in 2011, including by arming Syrian rebel groups.

Longtime Damascus ally Russia bolstered its military presence in Syria and launched a bombing campaign in late September that it said was aimed at keeping Assad in power and striking "international terrorist" targets.

Air strikes and other intense violence has continued in Syria despite a shaky "cessation of hostilities" agreed among international powers.

Amidror said rebels in Syria gained from Badreddine's death and that Israel also benefited.

Badreddine, who was on a U.S. terrorist blacklist, was one of four people being tried in absentia by a UN tribunal for the murder of former Lebanese Prime Minister Rafiq Hariri.

Hizballah did not provide details of Badreddine's death. The Beirut-based Al-Mayadeen TV, which is close to the group, initially said he was killed in an Israeli air strike -- though that report was later removed.

Hizballah lawmaker in Lebanon Nawar al-Saheli later on May 13 said he awaited the results of an investigation but added that "this is an open war" and "certainly Israel is behind this." He vowed that "the resistance will carry out its duties" in response.

Announcing Badreddine's death, Hizballah said in a statement, "He took part in most of the operations of the Islamic resistance since 1982."

An unnamed deputy leader of the group was quoted as saying on May 13 that Hizballah would "continue in the path" of Badreddine.

Russian officials did not immediately comment on Badreddine's death.

But Iran's foreign minister, Mohammad Javad Zarif, praised Badreddine in a letter of condolence as having "dedicated his whole life to the fight against injustice and terrorism," according to news agency ISNA.

Badreddine's death is the biggest blow to the militant group since the 2008 assassination of Badreddine's brother-in-law, Imad Mughniyeh, the chief of Hizballah's military wing who was killed in a bomb attack in Damascus.

"Today Hizballah is very much involved in Syria, and all its focus is in Syria," former Israeli official Amidror said. "But behind the corner, a year from now or a month from now, we might have to face Hizballah on the battlefield. If Hizballah has to go to the battlefield without a commander like Badreddine, it's better for Israel."

Amidror declined to speculate on whether Israel assassinated the commander.

Israel has assassinated Hizballah leaders in the past, including a 1992 helicopter strike that killed Abbas Musawi, the previous secretary-general of the organization. In December, militant Samir Kantar, who was imprisoned in Israel for three decades, was killed in an air strike on a residential building in a suburb of Damascus. Israel has also targeted convoys of Hizballah weaponry on the Lebanon-Syria frontier.

With reporting by Daniella Cheslow and AP, AFP, ISNA, and Reuters