Both civil war and a growing humanitarian crisis are already spreading from Syria into neighbouring Lebanon, provoking a backlash while threatening to engulf the wider Middle East.
Rocket attacks across the border into Lebanese territory are gaining in frequency, as are targeted bomb blasts within key cities such as Beirut and Tripoli.
As tensions heighten between Alawite, Sunni and Shia sects on either side of the Lebanese-Syrian divide, the country ruled by a fragile caretaker government is also troubled by a growing refugee influx.
Some 720,000 Syrian refugees have been registered with United Nations agencies in Lebanon, but credible estimates suggest as many as 1.3million may be spreading across a 4million-population nation.
Many are hesitant to make themselves officially known, for fear they could be traced by vengeful forces from Bashar al-Assad’s Syrian regime.
While Jordan’s 120,000-strong – and expanding – Za’atari refugee camp has compelled much attention, Lebanon’s Syrian refugee population is scattered much more disparately.
Some making it across the frontier – despite ever-encroaching Syrian military presence on Lebanese land – are paying rising rents for cramped basements or garages.
Many more are pitching makeshift tents in improvised campsites, many in the northern Lebanese region of Akkar or even closer to the border in hinterland Wadi Khaled.
The 40,000-population Wadi Khaled area has become a popular refuge for recuperating Free Syrian Army rebel soldiers – perhaps explaining the increasingly-regular bursts of border-crossing gunfire.
Tensions are rising not only among Assad loyalists keen to infiltrate neighbouring land, however, but also among Lebanon’s own deprived communities witnessing mass Syrian arrivals – and aid agency input, however limited.
The Lebanese government is now responding by ordering border officials to impose tighter controls on those flocking to flee Assad’s brutal 21-month crackdown.
Officers have been told only to allow across those with not only proper paperwork but also proof they are coming from towns and cities recognised as under-fire – despite the fact many refugees have been desperately shifting from area to area for months.
Canny landlords in regions such as Wadi Khaled have been hurriedly building extensions or new properties to accommodate refugees desperate for shelter – with rents rising all the time in response.
Yet those not fortunate enough to have property to let are suffering knock-on effects, with competition for jobs now more intense – and wages falling.
Newly-arriving Syrians anxious to afford shelter and food are said to be accepting wages of $1 per hour for tasks such as labouring or toiling in the fields – compared to the previous Lebanese average of $4.
Tensions have been exacerbated still more by the bursts of border shelling by Syrian forces and terrorist attacks carried out by brigades from both countries but on Lebanese land.
Shia militant group Hezbollah, which controls southern areas of the Lebanese capital Beirut, has thrown its weight behind the Assad regime – making it both a perpetrator and target of inner-city attacks.
There are even fears that Hezbollah could retaliate against any US-led air-strikes on Syria with attacks on arch enemy Israel – although such action could well provoke an even more fearsome response than the 2006 war between Israel and Lebanon.
Two almost-simultaneous mosque bombings on August 23 killed more than 40 people and wounded at least 500 in Lebanon’s second city, Tripoli – now home to the deported extremist, ‘Tottenham Ayatollah’ Omar Bakri.
Later that night a sniper stationed 50m from a school in Wadi Khaled opened fire – but the time of day meant no pupils or staff were present or injured.
That day’s attacks came a week after a car bomb in a Shia district of Beirut killed 27 people, with Syrian rebel forces cast under suspicion.
No wonder one anxious aid worker admitted to Metro: ‘There’s no house in Lebanon without a pistol, an M16 or a Kalashnikov. People are scared.’
Save The Children’s Lebanon director Sonia Zambakides said: ‘Lebanon has been very overlooked – it’s very much a crisis in its own right.’
Her charity is keen to direct what resources it has – and amid this week’s newly-launched £150million aid appeal – not only to struggling Syrian refugees but potentially-aggrieved Lebanese communities.
The constant chorus from Syrian refugees in Lebanon has been the desire to be able to go home.
For now, the main benefit of being in Lebanon is its relative safety – though that too looks increasingly uneasy and endangered.