Lebanon's Shiite Hezbollah movement, buoyed by the success of its fighters spearheading the landmark victory of the Syrian army in the strategic town of Qusayr last week, is now poised to take an even more assertive role in the Syrian civil war. But even as it flexes its military muscles across the border, Hezbollah is opening a very risky chapter that will determine the extent to which it can maintain its support base at home.

Fighting Arab Sunni Muslim regime opponents in Syria is a far cry from the Shiite movement's traditional raison d'etre: resisting Israel on Lebanese soil. Hezbollah has derived its legitimacy from its credentials of ousting Israeli occupation troops in 2000, battling Israel to a stand-off in the 2006 Lebanon war and being at the forefront of deterring what it trumpets as a continued Israeli threat. Being in Syria is a stretch of this, to say the least.

Fighting with the Syrian regime until victory over the "takfiris" or extremist Sunni Muslims, as Hezbollah leader Hassan Nasrallah recently vowed to do, is no simple matter for the Shiite group. If anything Hezbollah now seems to be laying bare what is at heart an Iranian proxy fighting on behalf of a regime vital to Iran's interests, rather than a Lebanese movement concerned about the well-being of its Lebanese Shiite constituency.

Once revered in the Arab arena for its stand against Israel, Hezbollah is now openly reviled by Sunni Muslim countries for its Syria intervention, seen as a sectarian push for Shiite Iran and its Alawite ally in Damascus, Bashar Assad. And the move has fueled a sectarian response. The influential Qatar-based Sunni cleric Youssef al-Qaradawi last week called on able-bodied Sunnis to go fight the Assad regime, Hezbollah and Iran in Syria. He termed Hezbollah "the party of Satan," a play on words of its name "party of Allah," while Saudi Arabia's grand mufti Abdulaziz bin Abdullah al-Sheikh labelled the group a "harmful sectarian party."

Even before clashes in Beirut Sunday over Hezbollah's Syria role, Nasrallah was accused of heightening sectarian tensions in Lebanon in a way that brings back horrific memories of that country's civil war.

Hezbollah is an organization that brooks no public dissent against Nasrallah. But Sheikh Subhi al-Tufayli, a former head of the group now estranged from it, sharply criticized the Syrian involvement in an interview with al-Arabiya television over the weekend: "Hezbollah's project as a resistance party that works to unify the Islamic world has fallen," he said, adding that it "opened the door for a ferocious period of sedition" in Lebanon.

Hezbollah also recognizes that its Syria surge is potentially dodgy at home. There is a campaign being waged by Nasrallah and by its al-Manar television station to sell the fighting against the Syrian opposition as a war against Israel and therefore a continuation of the resistance legacy. In this context Israel and the United States are lumped in Hezbollah pronouncements together with the "takfiri" fighters in a broad conspiracy against the "resistance axis" of Syria, Hezbollah and Iran. Thus, in reporting the Qusayr victory an al-Manar newscaster stressed that "Israel bet on the steadfastness of the [opposition] gunmen and was wrong. All the dreams and illusions have fallen. The Syrian army has sent a message to those participating in the aggression against Syria, foremost the Zionist enemy and its collaborators in the region."

And al-Manar gave prominence to a pro-Assad Syrian military analyst's assertion that the opposition forces in Qusayr were equipped by Israel.

Nasrallah, in his landmark May 25 speech vowing enduring support for the Syrian regime, said it was actually a battle for the existence of Lebanon."If Syria falls to American, Israeli and takfiri hands, the resistance will be surrounded and Israel will enter Lebanon to impose its conditions on the Lebanese and establish its projects anew," he said. Al-Manar's website Sunday quoted Nasrallah as framing the Syrian fighting as a battle for Palestinian rights: "If Syria falls, Palestine will be lost forever."

Al-Manar also deployed a Hezbollah-allied Sunni cleric in the southern city of Sidon, Maher Hamoud, to justify its Syrian intervention. Hamoud, who survived an apparent assassination attempt last week, said, as if on cue, "the takfiris are a danger to the Moslems. Hezbollah chose the least bad alternative in Qusayr. Hezbollah is always careful not to spread sectarian conflict or ignite it."

If Hezbollah's involvement translates into a relatively rapid victory for the Assad regime, Nasrallah will be able to fend off questions and Hezbollah's fortunes will rise in Lebanon. But if casualties steadily mount and the boomerang in sectarian conflict in Lebanon intensifies, Nasrallah could face a serious legitimacy crisis.

"Hezbollah's power comes from the strength of its narrative, which enabled it to justify its existence almost as a state within a state," says Nadim Shehadi, a specialist on Lebanon and Syria at the Royal Institute of International Affairs in London. "What it's doing in Syria is very easily challenged in legitimacy terms. It goes way beyond Hezbollah's definition of itself and involves its own community in something it doesn't want to be involved in."

Ben Lynfield writes from the Middle East for the Scotsman and other publications.

Image: Flickr/David Holt London. CC BY-SA 2.0.