This week, fierce clashes took place in Syria’s Homs province, close to the border with Lebanon, between Free Syrian Army fighters and armed men loyal to the Lebanese Hezbollah movement. The Lebanese Shi’a group used its positions in the Bekaa region to fire Katyusha rockets at FSA positions across the border.The Hezbollah-affiliated fighters, said by one local resident to number around 5,000 men, operate ostensibly to protect the Shi’a population. Some 30,000 Lebanese Shi’a live in 20 villages in the area.Hezbollah leader Hassan Nasrallah claimed that the gunmen were simply local Shi’a residents who had decided to take up arms to defend themselves without seeking the advice or permission of Hezbollah.There were few takers for this version of events. The Syrian rebels regard the Shi’a gunmen as simply another element in the force available to Syrian dictator Bashar Assad. Fahd al-Masri, a spokesman for the FSA, noted that rebel forces have observed the movement of large amounts of arms and ammunition across the border from Lebanon to Syria. The rocket fire from Hezbollah positions in Lebanon renders Nasrallah’s assertions entirely hollow.Rather, a growing body of evidence suggests that the events on the border are only a part of a much more significant Hezbollah presence among the pro-government forces in Syria.This includes, according to credible reports, an involvement by the movement in training efforts to turn the Shabiha militia into a more formidable force.The Alawi Shabiha irregulars are suspected of many of the most heinous acts of sectarian bloodletting which have marked the Assad regime’s attempt to destroy its opponents.The FSA now claims to be holding 13 Hezbollah prisoners, captured in fighting near the town of Qusayr, close to the border.Hezbollah’s actions on behalf of the Assad regime are serving to deprive the movement of the last vestiges of its claim to constitute a grass-roots, Lebanese “resistance” force concerned mainly with fighting Israel.Events in Syria have made plain what was never really in doubt: Hezbollah is a sectarian instrument of Iran which formulates policy and acts in accordance with the perceived interests of an Iran-led alliance.Domination of Syria enables Tehran to maintain its supply lines to its proxy on the Mediterranean. It is a vital interest for both the mullahs and their Lebanese clients.The Shi’a Islamist movement is therefore deeply invested in the struggle of Assad and the Iran-led interest to triumph over its foes.The resulting hatred of Hezbollah and Iran to be found in rebel ranks is deep and fierce.In Idlib province, in the areas from which the regime army has withdrawn, opposition activists hoard Hezbollah flags. Many were left behind from the 2006 war, when the Assad regime would deck the streets with them in solidarity with its ally in Lebanon. The opposition activists keep the flags in order to burn them during street protests.A fighter of the Sunni Islamist Tawhid Brigade in Aleppo city interviewed recently by this reporter refused to even pronounce the name of Hezbollah.Instead, he referred to the movement as “Hizb a-Shaytan” (the party of Satan).These sentiments, along with the widespread conviction that Iran and its local allies are the key factor in prolonging the bloodshed in Syria, are storing up an account which, in the event of their victory in Syria, the Sunni rebels are likely to seek to settle.Following the killing of senior Hezbollah commander Ali Hussein Nasif by the FSA in Homs province last month, the rebels vowed to take the fight to Hezbollah’s strongholds in south Beirut.Whether or not such action is imminent, the decision of where and when to strike is ultimately a tactical one.On a strategic level, Hezbollah is part of Assad’s “killing machine,” as US Ambassador to the United Nations Susan Rice recently and eloquently expressed it.Which means that whatever the tactical details, the FSA and Hezbollah are already in a state of war.Lebanon itself has stayed mainly free of direct violence related to the events in Syria. The exception has been the city of Tripoli, where Sunni Islamist supporters of the rebellion have clashed with Alawi partisans of the regime along a number of fault lines. These disturbances, while bloody, have been localized.But in the volatile Bekaa area, where Sunni and Shi’a populations live in uneasy proximity, each community actively aids its preferred side in the civil war across the border. Sunni villagers remember well the harsh conditions imposed upon them by the Syrian military during its long occupation of the area between 1990 and 2005. Many young men from this area have crossed the border to fight with the FSA.Shi’a towns, meanwhile, send operatives across the same border to fight for the other side. Ali Hussein Nasif, for example, came from the village of Bodai in the western Bekaa, a place of fervent pro-Hezbollah sentiment.Further afield, evidence has emerged of the involvement of senior politicians from the opposition March 14 coalition in efforts to supply arms to the rebels.All of which means that despite the relative quiet in Lebanon itself, rival Lebanese political forces are deeply invested in the outcome of the civil war across the border.The Sunni-led March 14 movement, and Lebanese Sunnis in general, clearly see the fall of the Assad regime as the key to ending the Shi’a ascendancy established by Hezbollah over the last half-decade.Hezbollah, meanwhile, is neither willing nor able to alter its basic nature as a client and proxy of Iran, to whom it owes its current dominance of Lebanon.It is therefore embarked on an all-or-nothing gamble on behalf of its masters. This gamble will end either with the eventual resurgence of the Assad regime – and with it, a strategic triumph for the Iranian interest in the Levant – or with the Syrian dictator’s destruction. The latter outcome may then bring down a fierce Sunni reckoning on both Hezbollah and the constituency it controls in Lebanon.Hezbollah, by its very nature, had no choice but to go down this road. Still, seen from this angle, the movement’s participation in the sending of a drone southwards over Israel this month looks like a rather plaintive attempt to change the subject. Hezbollah evidently sought to recall the days when its main military efforts were not directed against its fellow Arabs.But as the Syrian civil war threatens to burst its banks and erupt into Lebanon, those days look increasingly distant.