The Diab family can never return to Maaloula. Not since the Christians of this beautiful and sacred town saw their Muslim neighbours leading the armed Nusrah Islamists to their homes. Georgios remembers how he peered over his balcony and saw Mohamed Diab and Ossama Diab and Yasser Diab and Hossam Diab and Khaled Turkik Qutaiman – all from Maaloula – walking in the street with men whom he said were dressed in Afghan-Pakistani clothes. “One of them had a Kalashnikov rifle in one hand and a sword in the other,” he says, shaking his head in disbelief.

Twenty years ago, identical tragedies destroyed the villages of Bosnia. Now they are being re-enacted in Syria. “We knew our Muslim neighbours all our lives,” Georgios says. He is a Catholic. “Yes, we knew the Diab family were quite radical, but we thought they would never betray us. We ate with them. We are one people.

“A few of the Diab family had left months ago and we guessed they were with the Nusra. But their wives and children were still here. We looked after them. Then, two days before the Nusra attacked, the families suddenly left the town. We didn’t know why. And then our neighbours led our enemies in among us.”

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It is a terrible story in this most beautiful of towns, with its 17 churches and holy relics and its great cliff-side caves. Now the fighters of Jabhat al-Nusra – a rebel group with links to al-Qa’ida – are surviving in the caves and shooting down at the Syrian soldiers in Maaloula’s streets with Russian sniper rifles. You have to run from house to house, and one bullet smashed the windscreen of a parked car scarcely 10 metres from the balcony on which Georgios was telling his awful story. Up the road, a mortar round – apparently fired by Nusrah men – has torn a hole in the dome of a church. The Syrian army says it has driven the Islamists from Maaloula, which is technically true; but to leave the town, I had to ride in the back of a military armoured vehicle. It is not a famous victory for anyone.

Not one of the 5,000 Christian residents – nor a single member of the 2,000-strong Muslim community – has returned. Maaloula is, almost literally, a ghost town. Only Georgios and his friend Hanna and a few other local Christian men who joined the “national defence” units to defend their homes, are left. At least 10 Christians were murdered when the Nusra militia began its series of attacks on Maaloula on 4 September, some of them shot – according to Hanna – when they refused to convert to Islam, others dispatched with a knife in the throat. And there is a terrifying historical irony about their deaths, for they were slaughtered within sight of the Mar Sarkis monastery, sacred to the memory of a Roman soldier called Sergius who was executed for his Christian beliefs 2,000 years ago.

Hanna says that before the war reached Maaloula this month, both Christians and Muslims agreed that the town must remain a place of peace. “There was a kind of coexistence between us,” Georgios agrees. “We had excellent relations. It never occurred to us that Muslim neighbours would betray us. We all said ‘please let this town live in peace – we don’t have to kill each other’. But now there is bad blood. They brought in the Nusra to throw out the Christians and get rid of us forever. Some of the Muslims who lived with us are good people but I will never trust 90 per cent of them again.”

Could there be better evidence of Nusra’s desire – and that of almost every side in this conflict – to sectarianise the war? Georgios joined his armed government unit when Nusra gunmen returned two days later – on 6 September – and now carries a huge 75mm Czech pistol strapped to his chest. He fought alongside the Syrian army’s 3rd Armoured Division, which took three days to recapture Maaloula because, the soldiers say, they could not risk damaging the churches and shrines. And therein lies a major problem. A Syrian Second Lieutenant called Talal told me that the caves had now been surrounded and that the Nusra snipers would run out of supplies. But if this is true – given the number of bullets cracking down the streets during my visit – the insurgents still seem to have plenty of ammunition.

The problem, of course, is that there’s a simple military solution to Maaloula’s present agony: for the army to use shellfire from their Russian-made tanks to blow the caves to pieces. But that would only continue the destruction of the heritage of Maaloula, whose people still speak Aramaic, the language which scholars believe was spoken by Christ. Only five months ago, in an untouched Maaloula, I stood next to the church of Mar Taqla while a Catholic girl recited the Lord’s Prayer’s in Aramaic. No prayers now.

It is impossible, amid the bullet-whizzing streets of the town today, talking to armed Christians whose emotions are incendiary, to gather up the full – even accurate – story of the Maaloula tragedy. They say that the church of Mar Taqla has been badly damaged, the altarpiece smashed, Byzantine pictures destroyed, but even Syrian troops will not approach the monastery today. When they briefly tried to help some nuns return after the battle, they told me, Nusra snipers cut them down, many shot in the legs as they helped the nuns to run away.

Almost every soldier I met had been wounded. Lt Talal, who comes from Sweida, had been hit in both legs during the battles. Two Syrian soldiers were hit on Monday, one in the legs, another in the shoulder. From an earlier skirmish with Nusra men – apparently with another Diab brother – Georgios had been shot in the arm, legs and ribs, and one of his fingers had been torn off by a bullet.

The Nusra men seemed to take a perverse pleasure, not only in destroying Christian icons, but household beds and chairs, perhaps in a search for cash.

Even the exact number of deaths cannot be confirmed. But it is impossible to believe, after these sectarian wounds, that Maaloula can return as it was, a place of worship for Orthodox and Catholic but also, intriguingly, for Shia Muslims, many of them Iranians who used to visit the town to see its monasteries and Christian shrines.

A Syrian general tried to explain to me later that I was not witnessing a civil war, merely a “war against terror” – the stock government quotation – and that Syrians were not sectarian. “In Latakia, we have 200,000 Sunni Muslim refugees living among Christians and Alawites and there are no problems between them,” he said. This is true. And outside Maaloula, several civilians claimed that the Nusra forces which invaded the town – and which numbered 1,800 men, according to the Syrian army – also killed local Muslims.

For several days, the Nusra gunmen held out in the wreckage of the Safir Hotel before taking to the caves. The Christians are now all refugees, some in the Christian Bab Touma district in the old city of Damascus, others in Lebanon. But some statistics, however loosely gathered, speak for themselves. Sixty per cent of the Christians of Syria are now believed to have fled their country.