Sectarian divisions have simmered throughout Syria's 17-month-long uprising, but these lines have become increasingly pronounced as the political upheaval turns more violent.

In fact, Middle East experts worry that sectarian violence could explode if the Assad regime falls and retribution becomes the order of the day.

Here's a look at the religious groups that make up Syria:

Sunnis

Sunni Muslims account for 74 per cent of the entire Syrian population. They are in the majority in every part of the country except for southern Al-Suwayda and northwestern Latakia.

Ordinary Sunnis also comprise the bulk of the opposition to President Bashar al-Assad's regime. Some Sunni elites are among its supporters, but that support has been cracking, as witnessed in the recent round of high-level defections.

Defections from the armed forces have been largely by Sunni generals, according to reports. A high-level diplomatic defection in early July was also by a Sunni Muslim, the Syrian ambassador to Iraq, Nawah al-Fares.

Fares had served in the ruling Baath Party and as governor of Latakia, a region dominated by the minority Alawites, the Assad family sect that makes up much of the country's elite and general staff.

Assad's wife, Asma al-Akhras, is from a prominent Sunni Muslim family from Homs.

Alawites

The Alawites make up only 12 per cent of Syria's population of 22.5 million but they have dominated the country for the past four decades. The minority Shia Muslim sect celebrates certain Christian rituals, such as Christmas and Easter, which makes them seem like heretics to many Muslims.

The second largest religious group in Syria, most Alawites live in the northwestern Mediterranean port city of Latakia and nearby mountains. And there are also large numbers of them in some of the nicer areas of Damascus.

The Syrian president's father, Hafez, came from a poor Alawite family. With his rise to power in a 1970 coup, the fortunes of the Alawites also rose.

Hafez filled key political and military positions with fellow Alawites and today an estimated 70 per cent of the military's elite units is said to be made up of Alawites.

Many members of the feared pro-Assad militia called Shabiha are also from this minority religious group. "Most importantly, the key elements within the armed forces are made of the Alawite minority," observes Peter Fragiskatos of the University of Western Ontario. He says that a key sign of cracks in the regime would be defections from that group.

Though powerful in today's Syria, the Alawites were oppressed through much of their history. That changed when Ottoman rule ended with the First World War and France took over the mandate of what is now Syria and Lebanon and, some historians said, deliberately incited sectarian divisions to suppress Arab nationalism.

Christians

Christians constitute about one-tenth of the Syrian population, or about two million people. This religious group is divided into a number of churches, including Greek Orthodox, Greek Catholic, Syrian Catholic, Maronite and Protestant.

Many of Syria's Christians have not abandoned their support for Assad or their Alawite neighbours, fearing being ruled by an Islamist Muslim Brotherhood if Assad is overthrown.

However, Syria expert Joshua Landis, director of the Centre for Middle East Studies at the University of Oklahoma, noted to USA Today that there are also plenty of Christians in Syria who "believe that democracy in the long run is the best protection for Christians."