Free Syrian army members remove a body from rubbles from damage caused by what activists said was an airstrike with explosive barrels by forces loyal to President Bashar al-Assad in Al-Shaar area in Aleppo December 17, 2013. REUTERS/Molhem Barakat (SYRIA - Tags: POLITICS CIVIL UNREST CONFLICT)

Down and out: Members of the Free Syrian Army remove a body from rubble. The power of the Western-backed group is waning as new rivals emerge. Photo: Reuters

In the small room crowded with badly injured men in a Syrian ''recovery house'' in Turkey, Nasser stands out. He has lost a leg, an eye and three fingers on one hand, and his other badly burnt and shattered leg is held together with a gruesome metal brace that pierces his skin in at least eight places.

A commander in the rebel Free Syrian Army, he was injured when his car exploded in Hasaka province in eastern Syria - ripped apart by a bomb planted, he suspects, by a Kurdish militia known as YPG. It could as easily have been al-Qaeda.

Nasser is just one of thousands of casualties on the new front that has opened up in Syria's war - a bloody, messy battleground in which the opposition to President Bashar al-Assad's regime has splintered.

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With the Western-backed, largely secular Free Syrian Army (FSA) divided and scattered, the rebellion is being driven by two broad and competing groupings of Islamists.

One group, led by the Islamic State of Iraq and the Levant (known as ISIL or ISIS) and Jabhat al-Nusra, openly declares its allegiance to al-Qaeda and its cause of a global Islamic state.

The other group, the newly formed Islamic Front, is a coalition of militias seeking to establish an Islamic state within Syria's borders.

These groups - along with a host of smaller independent ones - are locked in a deadly game to win power and territory, while also fighting to overthrow the regime.

But as the ISIL and Jabhat al-Nusra recruit ever-increasing numbers of foreign fighters, some experts say the Islamic Front - formed last month - could represent the last hope of redirecting the Syrian revolution away from al-Qaeda and towards defeating the Assad regime.

The three largest groups in the Islamic Front - the Ahrar al-Sham, the Damascus-based Jaysh al-Islam (formerly Liwa al-Islam) and Aleppo-based Liwa al-Tawhid - are each bigger individually than ISIL, which is thought to have about 8000 members.

With more than 45,000 fighters, the Islamic Front is ''the last card in the pack'', says an observer. ''If they fail, the Syrian revolution is finished.''

The first casualty of their increasing power, the observer says, is the FSA.

The Islamic Front's actions last week indicate the FSA and its leader, General Salim Idris, have lost what little power they had left.

The Islamic Front took control of warehouses at the crucial Bab al-Hawa border crossing between Turkey and Syria, seizing weapons intended for the FSA and, reportedly, the headquarters of its Supreme Military Council.

In response, the US and Britain announced the suspension of all non-lethal aid to the FSA, while General Idriss fled to Turkey.

Charles Lister, a visiting fellow at the Brookings Doha Centre and an expert on Syria's Islamist groups, says the Islamic Front ''presents the best opportunity … to re-establish some Syrian authority over the armed opposition and to re-emphasise the original objectives of the revolution, which was to overthrow Assad''.

The Front could grow into a ''competitor to al-Qaeda'', he says, stemming the rising tide of Syrians joining groups linked to the terrorist network.

Until recently, 24-year-old Abu Khaled was a military commander with Jabhat al-Nusra in Hasaka city.

He is deeply critical of the FSA, for which he once fought, and openly supportive of the Islamic Front.

''The FSA were not organised, they did not have good security and they were not so strict in terms of morals,'' he says. So he joined Jabhat al-Nusra and rose quickly through the ranks, leaving only recently after a dangerous fallout with another commander.

He is in Turkey raising funds to build his own independent brigade, but like many disaffected rebels, he views the formation of the Islamic Front as positive. ''It is the best step in the Syrian revolution,'' he says. ''We need to avoid conflict between groups, and where the Islamic Front exists, it is not chaotic.''

Another rebel leader in the eastern town of Deir al-Zor, Abu Fahr, puts it simply: ''We have to create a third power beyond [ISIL] and Jabhat al-Nusra to keep the balance and represent the original aims and goals of the revolution.''

In the middle of a war between armies proclaiming their allegiance to the Islamic faith or the Syrian nation, a fight is also going on for the support of the country's tribes.

Three weeks ago, one US ally, the United Arab Emirates, convened a meeting of dozens of tribal leaders from the oil-producing region of east Syria that borders Iraq.

The extraordinary gathering was asked to consider the establishment of a Sahwa - or Awakening - movement, similar to the one funded by the US to fight al-Qaeda in Iraq, sources say.

In the face of the significant advances made by ISIL in the past six months, it was hoped a movement following the Iraqi model might temper ISIL's gains in Syria.

''Absolutely not,'' says Sheikh Nawaf al-Bashir, head of the prominent Baqara tribe and among those who attended the meeting in the UAE. ''I am against the Sahwa - I am Muslim, I will not fight against other Muslims.

''Tribes will fight the regime but they will not fight ISIS or Jabhat al-Nusra because it is too late - their sons are enrolled in these two groups and those who have not joined will soon follow. They will not fight each other, this will never happen.''

Concerned about talk that the UAE gathering had approved a Sahwa, the sheikh travelled to Syria two weeks ago. ''I went to Syria to prove it was a false rumour, to show that I would not fight,'' he says from his office in downtown Urfa.

Lister says the gathering of tribal leaders was unprecedented. ''All kinds of diplomatic manoeuvres are taking place, many of them pushed by Western states and other allies in the Gulf who have a specific interest in trying to grasp back some element of control of the conflict,'' he says.

''But I have some scepticism as to whether this [a Sahwa movement] has the same potential in Syria.

''Even though an argument can be made that the Sahwa was quite successful in pushing al-Qaeda out of a lot of urban centres in Iraq, al-Qaeda is still an extremely powerful organisation in Iraq and in many respects it is now taking its revenge against the tribes.''

Members of Syria's eastern tribes say that when groups linked to al-Qaeda first came to the country, they were careful to try to win over tribal leaders. This gave them a better chance of striking deals to control some of the oil and gas fields, one leader recalls.

Dozens of tribal leaders in Aleppo swore allegiance to ISIL several months ago. ''We have certainly got the jihadists attempting to acquire the allegiance of the tribes in Syria, just as we are seeing a fairly open initiative to try and acquire the support of tribal leaders to present a potential bulwark against jihadist organisations,'' Lister says.

As heavy snow fell on the border town of Kilis in southern Turkey, the local bus station - a hub for those travelling from Istanbul, the capital Ankara and elsewhere around the country - was buzzing.

Along with shivering Syrian families who had recently made the short but perilous journey across the border and out of Syria were men from Saudi Arabia, central Asia and Azerbaijan, heading for the fighting.

Most did not want to speak, but one Uighur man confirmed he was waiting for others to join him before they would be smuggled into Syria.

He is prepared to die for the cause, he says, ''for the Syrian people''.

He is just one of many Uighurs - a Sunni Muslim ethnic group that lives in eastern and central Asia, mostly in the north-west of China - fighting inside Syria.

Latest figures from the International Centre for the Study of Radicalisation indicate there are up to 11,000 fighters from 74 countries in Syria, double previous estimates.

''While Arabs and Europeans continue to represent the bulk of foreign fighters [up to 80 per cent], we have identified individuals from south-east Asia, North America, Australia, and [non-Arabic] Africa,'' writes Aaron Zelin, a fellow at the centre, which is based at King's College, London.

The five countries with the largest numbers of foreign fighters in Syria are Jordan (more than 2000), Saudi Arabia (approximately 1000), Tunisia (970), Lebanon (890) and Libya (550), the centre says.

Only 20 per cent of foreign fighters have declared affiliations, it says. Of those, the vast majority are with Jabhat al-Nusra and ISIL.

The rise in foreign fighters on the rebel side, Zelin writes, has coincided with the more open involvement of Hezbollah fighters from Lebanon, Iraqi Shiite militias and Iranian government forces fighting alongside the Syrian regime.

''This may have reinforced and strengthened the perception among some Sunnis that the conflict is fundamentally sectarian, and that Sunnis need to stand together in order to halt the [Shiite] enemy's advance,'' he adds.

The rate of foreign fighters arriving from southern Turkey had also spiked since the chemical weapons attack on the outskirts of Damascus in August, in which at least 800 people died.

With so many forces in the field, it is difficult to imagine how agreement will ever be reached on who, if anyone, will represent the ''Syrian opposition'' at the UN-sponsored talks due to take place in Geneva next month.

Meanwhile, the death toll rises by the hundreds each week as ever more civilians flee the country.

And winter has only just begun.