The bloodletting in Syria, where the United Nations estimates 30,000 people have been killed since March 2011, is pushing Lebanon, riven by deep-rooted sectarian rivalries, closer to the brink of another internecine war.
Amid a rash of alleged assassination attempts against Christian leaders, largely blamed on Syria's murky intelligence services, and the August arrest of a prominent Christian pro-Syrian figure on charges of plotting terrorist attacks at Damascus' behest, Lebanon's poised to become Syria's western front.
Both the Syrian regime of President Bashar Assad and the rebels use Lebanon to funnel men and arms into Syria.
Syria has launched artillery and airstrikes against Lebanese villages and suspected smuggling routes. Several Lebanese have been killed. Dozens have been kidnapped in retaliation for abductions inside Syria.
Heavily armed clan militias, some supposedly linked to Hezbollah, the powerful Shiite movement backed by Syria and its ally Iran, have materialized to grab hostages to exchange for co-religionists seized by largely Sunni Syrian rebels.
The Lebanese army, heavily infiltrated by Hezbollah and which has sought to remain on the sidelines of a steadily deteriorating security crisis, finally had to respond in September and carried out raids on the Shiite Miqdad clan to free captives it held.
The 55,000-strong military has also moved to crack down on smuggling of arms and fighters into Syria. But it's come nowhere near eliminating it -- and may not be able to.
"Because of the importance of the passes across the Anti-Lebanon Mountains, Syrian rebels and the Syrian regime will both continue to attempt to gain control of the mountain range," observed the U.S. global security consultancy Stratfor.
"If the Syrian rebels can drive regime forces from the mountains on the border, they would be able to threaten major regime supply lines running parallel to the border and would be in a better position to affect the ongoing battle in Damascus.
"Sunni fighters and supplies streaming into Syrian from Lebanon could significantly bolster rebel efforts both in Damascus and the Orontes River valley."
That would force the Assad regime to redeploy sizeable forces now in the north and east to Damascus, and significantly ease the pressure on the rebels on various fronts.
Support for the Syrian rebels is strong in northern Lebanon, long a sectarian flashpoint.
Sunni and Alawite militias have repeatedly clashed in the northern capital of Tripoli, leaving dozens of dead and wounded.
Beirut, a key battleground in Lebanon's 1975-90 civil war, has avoided such bloodshed -- so far. But there are menacing rumbles, with pro-Syrian factions increasingly looking for trouble.
Caught in the middle of this anarchy is Hezbollah, the creature of Iran's Revolutionary Guards and Syria's most powerful Lebanese proxy.
There have been persistent reports Hezbollah has sent "military advisers" to Syria. One report has them training "divisions" of paramilitary fighters from the minority Alawite sect that dominates the Damascus regime.
The reports are impossible to verify. But it's likely Hezbollah has a military presence in Syria over and above the garrison it maintains in the border town of Zabadani to funnel weapons into Lebanon.
Since Tehran seeks to use Hezbollah to attack Israel in the event the Jewish state launches pre-emptive strikes against Iran's contentious nuclear program, it's unlikely Tehran would release significant numbers of Hezbollah veterans to fight anti-regime forces in Syria.
But either way, Hezbollah has found itself caught in any awkward position as Syrian rebels escalate the war while Lebanon struggles to avoid being dragged into the conflict.
If Hezbollah has been involved in the recent clashes, observed Oxford Analytica, "they indicate how pressured its leadership is by events in Syria.
"The Syrian leadership has a history of fomenting trouble in Lebanon to divert attention from domestic affairs.
"Damascus may calculate that a destabilized Lebanon will lessen U.S. and Turkish momentum toward imposing a no-fly zone in northern Syria and supplying the rebels with heavier weapons."
Meantime, Lebanon's Hezbollah-dominated government, set up in July 2011 and the fulfillment of the Shiite movement's political ambitions so far, is tottering near collapse because of the divisions exacerbated by the Syrian war.