Lebanon is getting dragged into the Syrian civil war. Continual violence from the fighting in Syria has spread into different Lebanese communities in its northern region, but this week there was a dangerous escalation when the Syrian army sent its helicopters into Lebanese airspace over the town of Arsal, which it then attacked with rockets, wounding one person and causing extensive damage. The Syrian regime claimed the residents had been supporting Syrian opposition fighters.

The attack has infuriated the normally supine Lebanese forces, who have said they would immediately respond to any further cross-border attacks. Lebanese President Michel Sulaiman has said that the “continuous shelling of Arsal by Syrian helicopters is a breach of Lebanon’s sovereignty and territorial integrity”, although he is not expected to make too much of a fuss as the Lebanese government does not want to irritate its much larger neighbour too much.

What happened last week is only one example of something that could spread and rip Lebanon apart. Arsal is a mainly Sunni town in Lebanon close to the Syrian border, where most residents support the rebellion against Syrian President Bashar Al Assad, and it is host to dozens of Syrians who were wounded in the bitter fighting as the Syrian government captured the opposition stronghold of Qusayr. However, just a few miles from Arsal, the largely Shiite town of Hermel has been used as a base by large numbers of Hezbollah fighters, who fought for the Syrian government in Qusayr.

Sectarian differences are inflamed by such violence. Deeper inside Lebanon, street fighting between armed supporters of different religious groups led to dozens of people in the northern city of Tripoli being killed, and two rockets were fired last month towards Hezbollah-controlled south Beirut. The Lebanese government has the difficult task of enforcing peace on truculent Syrian refugees and its own population, even as large numbers of fighters are treating Lebanon as an operating base. But if it fails, it knows that the terrible damage that war causes will engulf Lebanon again.