A Canaanite city that was mentioned in the Bible, Izraa has lived through Persian and Arab rule, with St Elias’s Church being built in 542AD – 28 years before the birth of the Prophet Mohammed in Mecca.

During the past four years of Syria’s war, its Christian population has largely stayed put, despite the war destroying much of the surrounding province of Deraa.

In the last two weeks however, men from the al-Qaeda linked Jabhat al-Nusra and other rebel groups have captured the nearby towns of Nawa and al-Sheikh Maskin, bringing the frontline to less than two miles away. They are now trying to assault Izraa.

Some of the rebels were vetted by the CIA as "moderate Muslims" and subsequently trained and armed in Jordan, as part of a US-led program to bolster a non-sectarian opposition to President Bashar-Assad.

But past experience has rendered such distinctions irrelevant to Izraa’s Christians. After all, in Syria – and on this frontline – the "moderates" continue to work in alliance with Nusra. And the conquest of other Christian villages by the opposition has shown that more moderate factions frequently do little to stop the jihadists imposing their will.

"It’s simple," said Father Elias Hanout, 38, who led the prayers at Sunday’s service. "If the West wants Syria to remain a country for Christian people, then help us to stay here; stop arming terrorists."

The pews were sparsely occupied for last Sunday’s service in St Elias, with the choir missing its tenors and altos. Mrs Azam, who led the hymns, was reluctant to acknowledge the exodus at first, saying the singers were absent "because of work". But as the tempo of the falling shells increased outside, she admitted: "People from here are leaving. Many are applying to emigrate."

Exactly how many Christians have left Syria is difficult to say, but according to the Christian charity Open Doors, some 700,000 have left the country, which equates to some 40 per cent of Syria’s pre-war Christian population.

Christian leaders in the country warn of an exodus on the scale of Iraq, where the 1.5 million-strong community that lived there prior to the first Gulf War is now down to as little as a tenth of its former size.

The threat to towns like Izraa will be uppermost in the mind of the Pope during his visit to Turkey this week, amid warnings from Christian leaders worldwide that their religion might soon lose its foothold in the very region where it was born.

Looking around his 1,500 year old church, Mr Hanout warned: "In this land the Word started. And if you delete the Word here, then Christianity across the world will have no future."

Evidence of the Church’s heritage is everywhere in Izraa’s narrow streets. Across from St Elias, lies the chapel of St George, an octagonal stone building that is said to be one of the most ancient churches in the world. Dating to 515 AD, it was originally converted from a pagan temple, and an inscription on its stone lintel reads: "Hymns of cherubs replaced sacrifices offered to idols and God settles here in peace, where people used to anger him."

Today, Izraa remains a mixed down of both Christians and Muslims. And in early 2011, when the uprising in Syria was defined by popular protests rather than war, a small number of Christians had welcomed the calls for regime change.

That changed when the Islamists began to dominate the rebel ranks.

"Nobody wants these men to advance," said one resident said, who asked not to be named. "They are frightened of their town being overrun by Islamists,"

Instead Izraa’s Christians have sought solace in the government’s defences, and increasingly blame the West for their suffering.

Mrs Azam added: "When evil comes you have to defend your country. We love our government, just as we love our country."

The picture in Izraa is one repeated across other Christian pockets of Syria. Christian homes in Deir Ezzour, Raqqa, and in Hassakeh, home to the Syriac Christians, the oldest denomination on earth, are all devoid of their inhabitants. From Homs too, a major Christian stronghold, many have left.

Some Christian residents initially remained in the Christian town of Ghassaniyeh in northern Latakia province when it first fell to the rebels in mid-2012. A few weeks later however, Islamic extremists took control of the terrain. Christian men were kidnapped, captured or forced to flee. They desecrated the church, ransacked homes and murdered the priest.

Even in Bab Touma, the Christian quarter in the old city of Damascus, residents told the Telegraph they were looking to leave.

Eva Astefan, 43, said she applied to the United Nations for asylum, after her 14-year-old daughter, Adel was shot and killed by a rebel sniper in 2012.

The family had been driving down the highway back to Damascus after attending the "Feast of the Holy Cross" in nearby Maaloula, when a hail of bullets pierced their vehicle, one entering her daughter’s skull who was sitting in the back.

Mrs Astefan’s nephew, Joseph Haroun, 29, said: "Its our country and we love it, but we feel we have little choice.

"The terrorists – referring to the opposition rebels – kidnap and kill our men and dangle the holy cross over their bodies."

It is not just Christian’s who are suffering. The war in Syria is political as well as sectarian, and, as it draws closer to Izraa, the town’s schools and municipal offices have become impromptu shelters for thousands of refugees from all sects.

Only a small number of the fighters near Izraa are from Nusra, with many of those fighting coming from local Sunni families.

Abo Mohammed, a frail Sunni man in his early sixties – who spoke using a pseudonym – told how of men who were his neighbours, fellow Sunnis, killed his "whole family" in revenge because his son is serving in the Syrian military.

"They entered our house in al-Sheikh Maskin and attacked my son, my brother, my brother’s children and my nephew. They broke their arms and legs and then threw them from the roof. I am the only one who escaped," he said, tears welling in his eyes.

It is precisely because al-Qaeda is weak in the south of Syria, that the West and its allies have concentrated on sending weapons to rebels in this area.

Residents from other sects have been able to return to their homes, even when they are in rebel control, but Christians fear that if they leave and their town is then captured by the opposition – even one led by western trained groups – they will never be able to return.

So, they put their hopes in the Syrian military that is now protecting the town. At the main entrance to the town are sandbagged army checkpoints, plastered with posters of President Bashar al-Assad. Military vehicles, laden with weapons, drive full-pelt across the intersection down the road that marks the beginning of the frontline.

In Izraa, shop fronts have been painted in the Syrian flag to rouse nationalist fervour, the graffiti of past anti-government protests has been scrubbed out or painted over.

Instead, the sense is of having been abandoned by other "Christian nations" such as America and Britain, no matter what the promises of their leaders are.

As another priest in Izraa, who asked not to be named, put it: "Please tell Mr Cameron, we don’t want any help or donations – but please, equally, stop arming terrorists."