Hezbollah plunges deeper into Syrian conflict
The overt involvement of Hezbollah fighters in the battle for the strategic western Syrian town of Qusair confirms the transition of the militant Lebanese Shia movement into a whole new phase of its existence.
From its inception as an Iranian- and Syrian-backed counter to the Israel invasion of Lebanon in 1982, Hezbollah's main focus was on resistance to Israel.
Its campaign against the Israeli occupation of southern Lebanon culminated in Israel's decision to pull its troops out of Lebanon altogether in 2000.
The month-long war between Hezbollah and Israel in 2006 gave the movement heroic status throughout the Arab and Islamic worlds for its extraordinary performance as an Arab David against the Israeli Goliath.
But less than two years later, in May 2008, that lustre dimmed sharply as Hezbollah did something its leader said it would never do - it turned its weapons against fellow Lebanese.
Stung by provocative positions taken by Sunni and Druze leaders, Hezbollah overran many Sunni areas in a short-lived conflict that reflected and exacerbated both rising sectarian tensions between Sunnis and Shia in Lebanon and the region; and divisions between the movement's Iranian and Syrian patrons on the one hand, and Saudi Arabia, other Sunni powers and their allies on the other.
'All systems go'
Now, those regional, political, strategic and sectarian issues have come to a head even more forcefully, as Hezbollah plunges deep into a Syrian civil war that is only tangentially related to its basic struggle with Israel.
The dangers for Hezbollah are obvious - that it may be drawn ever deeper into a bottomless pit of conflict in Syria that could leave it severely depleted and easy prey to a death-blow from Israel, although Hezbollah leader Hassan Nasrallah has dismissed that possibility.
"Yes, it's a risk for Hezbollah, but it's part of Iran's overarching regional strategy: the Syrian regime must not fall," said one well-placed Shia observer.
"It's all systems go, and Iran will unleash everything it has to. It and Hezbollah consider this a threat to their political existence."
"Israel's interest is to see the civil war continue and Hezbollah sucked in and massacred as it has been in the past few days, when they've lost 40 fighters. It's a grinding machine, and Israel is laughing and happy."
Indeed, put like that, it is hard to imagine Israel not being happy to see what it regards as extremists and terrorists from both the Shia and Sunni sides of the sectarian divide at each other's' throats in Syria.
Apparently foreshadowing Hezbollah's deepening involvement, Hassan Nasrallah in a speech on 30 April made it clear that Syria's allies in the "Axis of Resistance" - Iran and Hezbollah - would do everything necessary to save it.
"Syria has true friends in the region and the world who will not allow it to fall into the hands of the United States, Israel, or the takfiri [Sunni extremist] groups," he said.
"If the situation gets more dangerous, states, resistance movements and other forces will be obliged to intervene effectively in the confrontation on the ground."
'Party of Satan'
That seems already to be the case, at least as far as Hezbollah is concerned, reflecting the existential situation faced by the Syrian regime.
Some Western diplomats believe that much of the recent progress scored by regime forces against the rebels is down to active involvement by Hezbollah, whose expertise in street fighting surpasses that of the conventional Syrian army.
"It is an obvious sign of crisis for the regime that Hezbollah and the new National Defence Force should play such a big role in the key attacks at Qusair and east of Damascus," said one.
The National Defence Force is a recently-formed "Home Guard" militia believed to have around 50,000 personnel and to be trained, paid and armed by Iran and Hezbollah and drawn largely from the mainly Alawite "Popular Committees" and shabiha militia.
The exact extent of Hezbollah involvement on the ground is the subject of much speculation and mystification.
But its casualties on the first day of the attack on Qusair on Sunday, with around 30 reportedly killed on that day alone, were roughly double the estimate given for those of actual regime forces.
Standing over the body of one of the dead Hezbollah fighters, a rebel commander declared: "Let the whole world know that we are fighting Iran, and Russia, and Hezb al-Shaitan ["the Party of Satan" - Hezbollah means "the Party of God"], and the regime, while the world has abandoned us and gives us neither arms, ammunition, equipment nor men."
But it is hard to imagine Hezbollah enabling the regime to restore its control over the entire country.
While government forces have been making advances in some key areas, the rebels have also been gaining ground in other places and control large swathes of territory in the north, east and south.
If military stalemate should lead to some kind of fragmented equilibrium, Hezbollah's help in controlling the Qusair area, with its 20 or so Shia villages inhabited by many Lebanese nationals, would be vital to the regime's ability to protect the link between Damascus, the main cities to the north, and what is seen as the Alawite heartland along the north-west coast.
In Qusair, Hezbollah finds itself in a head-on collision not just with the Sunni-majority Syrian rebels and al-Qaeda-related Salafist fighters, but also with fellow Lebanese - Sunni jihadist militants come to join the fray.
Lebanese politicians - well aware of their country's sectarian splits and potential for civil strife - agreed a year ago to keep Lebanon out of the Syrian conflict and try to stay neutral.
With militant Lebanese Sunnis and Shia killing one another just across the border, how long can an explosion in Lebanon itself be averted?
Some key flashpoints have already been ignited, especially in the northern city of Tripoli, where an Alawite minority has for decades been at odds with Sunnis living in adjacent areas.
But Tripoli had already been spluttering into occasional flare-ups which have so far been isolated and contained.
Elsewhere, the number of friction points between Sunni and Shia areas is limited to a few places in the Beqaa Valley, on the southern edge of Beirut, and at Sidon in the south.
That is not to say that a wider flare-up might not happen - but after fighting a 15-year civil war in which nobody won and everybody lost, the main Lebanese factions seem loath to allow it to happen again.
But the loose cannons, relatively new to the Lebanese scene, are the militant Sunni Salafists, who are becoming strong in Tripoli and Sidon in particular.
Although comparatively few in number, there are fears that they might resort to the kind of provocative, indiscriminate car or suicide bomb attacks carried out so devastatingly by al-Qaeda or its affiliates in Iraq and Syria.