On a main road connecting the Lebanese capital with the south, Sheikh Ahmad Assir kneels under a blazing sun to pray and then sits down with supporters at his anti-Hezbollah protest camp and launches into a new tirade against Lebanon’s most powerful and well-armed force.

“By God, Nasrallah, I will not let you sleep at night,” he vows in a fiery speech, addressing Hezbollah’s leader, Sheik Hassan Nasrallah.

Few in Lebanon have dared take on the militant group in such a public way, but Assir, a hardline Sunni cleric, senses weakness. He sees a chance to push back against Hezbollah’s domination of the country’s politics.

The growing popularity among some Sunnis of the previously little known local cleric is a sign of how vulnerable Hezbollah has become as it faces the possibility of the downfall of its crucial ally, President Bashar Al-Assad in Syria.

Its reputation as a popular resistance movement has already taken a severe beating for siding with Syria against the anti-Assad uprising even after it supported Arab revolts in Egypt, Tunisia, Libya and Bahrain.

“This is the start of what will become Lebanon’s Tahrir Square,” Assir, wearing a long robe and white skullcap, told The Associated Press at his protest site, where some 150 Sunni conservative supporters have been camped out for some three weeks. “They have humiliated us for long enough. It’s about our dignity now. I can’t live like this, it’s enough.”

Assad’s fall would be a nightmare scenario for Hezbollah. Any Sunni-led new regime would likely be far less friendly to the group, or even outright hostile. Regime change could cut off a major supply route for Hezbollah’s weapons, heavily damage its political clout in Lebanon and knock out a third of the “Iran-Syria-Hezbollah” axis of “resistance” to Israel.

Nasrallah admitted how crucial the alliance with Damascus is in a speech Wednesday night after Assad’s regime suffered its hardest blow yet in the conflict — a bomb blast that killed three major regime figures, including the defense minister and Assad’s brother-in-law.

Nasrallah called the Syrian regime a “bridge” and a “critical support” for Hezbollah’s “resistance” against Israel. “The most important weapons with which we fought Israel in the July war came from Syria,” he said, in reference to Hezbollah’s month-long 2006 war with Israel.

In the face of the Syria crisis, Hezbollah is treading carefully to retain the power it has built up over the past 30 years in Lebanon, a deeply divided country where its strength is resented by Sunnis and some in the Christian community.

The group’s main strategy for doing so appears to be to lay low and avoid aggravating the volatile fault line between the Sunni and Shiite communities, which each make up about a third of Lebanon’s population of 4 million.

Lebanon’s sectarian tensions have already been worsened by the crisis in Syria, where the overwhelmingly Sunni opposition is struggling to oust a regime dominated by Alawites.

Regional shifts also weigh on Hezbollah. The so-called Arab Spring sweeping the Middle East has so far led to the rise of conservative Sunni Islamists deeply resentful of Shiite powerhouse Iran and its allies Syria and Hezbollah.

“Hezbollah has accepted that this is going to be a protracted crisis in Syria and by virtue of that, the group has been much readier to calibrate and reduce its footprint,” said Aram Nerguizian, a visiting fellow at the Center for Strategic and International Studies in Washington.

Over the course of Syria’s 16-month-old uprising, he and other analysts have noted a subtle shift in Hezbollah’s public position. Early on, Nasrallah embraced Assad, casting him as a reformer in speeches that infuriated Syrian protesters. He has since then somewhat modified his stance, calling on both sides to cease the violence and engage in dialogue.

Assir’s rapid rise and growing following are symptoms of the deep frustration among Lebanon’s Sunnis who resent the Hezbollah-led Shiite ascendancy to power in Lebanon. The 44-year-old, bespectacled, skinny cleric with a long bushy beard was previously little known, a preacher at the Bilal Bin Rabah Mosque in Sidon. Now he is openly challenging and taunting Hezbollah like few have dared before, even taking aim at Nasrallah, a revered figure usually considered a red line in Lebanon. Assir calls his protest camp an “uprising” against Hezbollah’s weapons, aimed at bringing the powerful arsenal of the group’s guerrilla force under the control of the government. Hezbollah, the country’s strongest armed force, has resisted pressure to do so for years.

Assir set up the camp blocking a main road in the southern coastal city of Sidon. The city is the gateway to Hezbollah’s traditional stronghold in the south and links the group’s command center in Beirut’s southern suburbs with front line villages in the south.

Sunni bitterness still runs deep over clashes in May 2008, when Hezbollah gunmen swept through Sunni neighborhoods in Beirut after the pro-Western government of that time tried to dismantle the group’s crucial telecommunications network. More than 80 people were killed in those clashes.

Hezbollah has not directly commented on Assir’s tirades and has gone into great lengths to rein in members who might clash with his supporters.