"The Sunnis remain dominated by [Hezbollah] and its weapons. We are vulnerable in particular," he told Foreign Policy at his office in Sidon. "If this continues, there will not be a war in Lebanon. There will be an attack on the Sunnis and they will not last one day."
Assir sees the Syrian regime and Hezbollah as working to advance Shiite domination of the region, and warns that Lebanon's Sunnis will be at risk as long as Assad lives. "Most people in the region are Sunni and refuse the Iranian project [of keeping Assad in power]," Assir says. "In [Lebanon], the Sunnis have been disappointed by successive governments. There is a glitch here and all parties need to be aware of it."
The rise of Assir -- and many more like him -- has been made possible by the prolonged absence of former Prime Minister Saad al-Hariri, who had previously been the undisputed leader of Lebanon's Sunni community. But after Hariri lost the premiership in June 2011, he departed the country for Paris amid rumours of money troubles and concerns for his safety, and has yet to return. As one Sunni fighter explained lamely when asked what connection his community has with its former standard-bearer, "he communicates with us over Twitter."
With Hariri gone, pro-Assad sources have accused countries sympathetic to the Syrian revolt of using Lebanese jihadist groups for their own purposes. As one high-ranking Lebanese Shiite political source termed it, the governments of Saudi Arabia, Turkey, and Qatar "insist on continuing to send fighters and snipers through Lebanon" and into Syria.
The State Department currently lists seven officially designated terrorist groups as operational inside Lebanon. One is the Shiite militant organization Hezbollah, but most are radicalized Sunni groups with alleged links to al Qaeda.
Their operations over recent years have been limited to smash-and-grab attacks. They were accused, for example, of being behind the roadside bombings in 2011 that targeted U.N. peacekeeping patrols in south Lebanon.
But now, emboldened by the outbreak of violence in Syria, several groups appear to be expanding their operations. Lebanon's tenuous security situation, not to mention its virtually non-existent border with Syria, allow the groups to launch jihadist operations against Assad - and also threaten his supporters closer to home.
Aaron Zelin, a fellow at the Washington Institute for Near East Policy, estimates there are currently at least 600 Lebanese fighting alongside rebel groups inside Syria. And he warns this will eventually boomerang back on Lebanon.
"We have seen this before with conflicts in the past -- which are termed jihad -- that when fighters in other countries come home it leads to destabilization," Zelin said. "And Syria is the most popular jihadist conflict in a while."