BEIRUT (Reuters) - Regional powers are pouring in money and guns, jihadists are joining rebels battling to overthrow Bashar al-Assad, while his own well-armed but hard-pressed forces are fighting back ruthlessly with combat aircraft and artillery.
Gruesome scenes of slaughtered civilians or executed rebel fighters provide daily snapshots of the worsening conflict in Syria. Video apparently showing rebels gunning down Assad militiamen in cold blood suggests the insurgents are capable of brutality to match their enemies.
After almost 17 months of revolt against the Assad dictatorship, Syria's conflict is turning into a regional proxy war between Sunni and Shi'ite Islam that could splinter the country along sectarian lines unless a unified rebel leadership emerges as a credible opposition to the beleaguered government.
Few observers of Syria see any sign of an opposition ready to run the country if or when Assad and his clan, whose power base lies in the esoteric Shi'ite sect of Syria's Alawite minority, lose overall control.
Some fear a Lebanon-style free-for-all, in which armed groups from different sectarian and ideological backgrounds fight for supremacy over territory, turning Syria into a patchwork that condemns its state to failure.
With the Shi'ite Islamic Republic of Iran behind Assad, and Saudi Arabia and other Sunni Muslim states backing the rebels, Syria could become the arena in which the regional Sunni-Shi'ite cold war becomes an open-ended civil war with the potential to destabilise its neighbours - Lebanon, Turkey, Iraq and Jordan.
"We most definitely have a proxy war in Syria," says Ayham Kamel of the Eurasia Group political risk consultancy. "At this point of the conflict it is difficult not to say that the international dimension of the Syrian conflict precedes the domestic one."
"Syria is an open field now. The day after Assad falls you (will) have all of these different groups with different agendas, with different allegiances, with different states supporting them yet unable to form a coherent leadership."
What started on March 15, 2011 as an internal uprising against the Assads' repressive 40-year rule, emulating the revolts that toppled leaders in Tunisia, Egypt, Libya and Yemen, has now been transformed into an arena for foreign meddling.
Kamel believes Syria is already fragmenting, and that the Free Syrian Army, the umbrella for a plethora of armed groups fighting to overthrow Assad, is little more than a franchise of Sunni Muslim groups.
"The Free Syrian army is only a slogan. There is no unity in these rebel groups," he argues. "To have an FSA you would need a command structure, and everybody following that command structure." Instead, he says, "There are different groups supplied financially and militarily by different states and they are quasi-independent."
"Different regions are controlled by different groups, whether of ideological or sectarian background, and whether Bashar's regime remains a player, we already have a lot more players than before," Kamel says.
"I don't discount the possibility that you (will) have different rebel groups struggling with each other for control of territory."
Close watchers of Syria say the real danger is of a prolonged and very bloody civil war and a sectarian struggle, exacerbated by the lack of a unified and credible opposition.
"I don't think there is anybody to take over," said George Joffe, a Middle East expert at Cambridge University. "The really big problem is that there is no credible opposition."
"How do you bring them together, how do you get them to collaborate at this late stage because they are diametrically opposed on what should be done?" he said.
Sarkis Naoum, a long-time critic of the Assad dictatorship who writes for Beirut's an-Nahar newspaper, says: "The opposition is fractured, with some outside and some inside (the country), some are Islamists, some are secular, but it is not easy to have an organised opposition with a government-in-waiting after 40 years of totalitarian rule."
"Any perception that a post-Assad Syria will involve a smooth transition is misplaced," insists Ayman Kamel.
RIDDLED WITH RIVALRIES
The political opposition in exile, represented by the Syrian National Council, which groups the Muslim Brotherhood, pro-democracy activists and leftist groups, is riddled with ideological and religious rivalries impeding its attempt to forge a political alternative to Assad.
While the SNC has been an international voice for the opposition, rebel commanders on the ground say the exiled leadership has little connection to what is happening in Syria.
The disarray among the opposition is on display in the contradictory statements on how to deal with the conflict, with some groups calling for more arms while others demanding a negotiated settlement.
As soon as some prominent SNC members announced the formation of a new political coalition that plans to establish a post-Assad transitional government, it was attacked by both the head of the SNC, Abdelbasset Seida, and the commander of the Free Syrian Army, General Riad al-Asaad.
Seida said: "If each group came out alone announcing the formation of a new government without talks, this would end up in having a series of weak governments that don't represent anyone." Asaad called the new coalition "opportunists" seeking to benefit from the rebels' gains.
On the ground, the picture is getting darker. State authority is slowly and incrementally disintegrating. Many areas of Syria are outside government control, regionalism is taking over from national unity, and rebel groups are multiplying with very different agendas and leaderships.
The government military onslaught has been stepped up since insurgents took their battle to Damascus and Aleppo last month and carried out a bomb attack against Assad's inner circle that killed his brother-in-law and three other top military leaders.
The conflict has left 18,000 dead and displaced hundreds of thousands, according to United Nations and activist figures.
It is complicated by Syria's religious divisions. The Assads and the military elite units belong to the Alawite sect, a minority in a Sunni Muslim country. The Alawites form about 12 percent of Syria's 23 million people but are reckoned to make up 40 percent of the army and the bulk of the pro-Assad Shabbiha militia. Sunnis, who account for the majority of the opposition, form 75 percent of the population.
Although the authorities have the upper hand because of superior firepower and units of loyal elite troops, the insurgents are highly motivated combatants who are becoming better armed, better trained and better organised.
As the conflict rages on without any solution, Syrians say homegrown Islamist jihadists and groups of fighters from al Qaeda have been taking an active role.
Most analysts agree that there is no "good or happy scenario" and that the chances of a negotiated settlement under the auspices of U.N. envoy Kofi Annan are nil.
Assad's forces' success in retaking insurgent-held territory in Damascus by using airpower, and their ferocious campaign in Aleppo, show the government still has the capacity to fight back and hold its ground, but most analysts believe it will find it difficult to sustain the momentum in the long-term.
Some think the authorities have prepared a fall-back position as an insurance policy should Assad's rule collapse: a retreat to an Alawite enclave on the north-west coast after expanding it by sectarian cleansing of some cities including Aleppo and Homs.
"I believe (the regime) has already begun to plan such an eventuality but that will set up a much wider conflict inside Syria itself," said Joffe.
"Aleppo is part of their focus to cleanse this coastal area, absolutely to clear it up to the Turkish border. I am sure that's the plan but whether they can do it or not it is something I don't know."
Such an enclave, coupled with the flow of refugees across the border and rising sectarian tensions in the region, could have effects beyond Syria to Lebanon, Turkey and Iraq, which have their own sectarian and ethnic mixes of Alawites, Sunnis, Shi'ites and Kurds and where tensions are already high.
With no Western appetite for military intervention and no prospect of an internationally mediated political resolution, many see the civil war spreading and tearing the country apart.
"Disintegration of Syria is a possibility and the problem is it won't work. It would create a power vacuum in which others get dragged in just like Iraq. It is a very frightening scenario," Joffe said.
Lebanese columnist Rajeh Khoury predicted: "Syria could plunge into a long protracted civil war that could last years. The civil war in Lebanon, with its much smaller population of five million, lasted 15 years due to foreign interference so Syria would be much more complicated.
"The Syrian crisis is so inflammatory that its flames will affect the region in one way or another."
(Additional reporting by Layla Bassam; Editing by Giles Elgood)