The Syria war is escalating in tandem with intensified diplomacy, but neither growing foreign military intervention nor a revived political track look capable of bringing an end to the 4-1/2-year-old conflict.
The risk is a more ferocious proxy war between President Bashar al-Assad's main allies - Russia and Iran - and Saudi Arabia, Turkey and the United States - which back rebels fighting to topple him.
The downing of a Russian warplane over Syria by Turkey has raised tensions, complicating the U.N.-backed political process just launched in Vienna that already faced big challenges.
Militarily, nearly two months of Russian air strikes twinned with army ground offensives backed by Iranian forces and Lebanon's Hezbollah have shored up Assad in western Syria. The Russian-backed ground offensives have made gains in Latakia province near the Turkish border, and in southern Aleppo. But they have not tipped the war decisively Assad's way.
Assad's enemies in the rebellion, pummeled by Russian bombers, have meanwhile received new foreign military support of their own, notably more U.S.-made TOW anti-tank missiles from Saudi Arabia that helped them stave off assaults in some areas.
Rebels were shown using one of these missiles to destroy a Russian helicopter grounded on a rescue mission to try to help pilots from the downed warplane, capturing the international dimensions of the war. A Syrian military source told Reuters the weapons are being used extensively and are having an impact.
The rebel cause could receive a political boost if a Saudi-led effort succeeds in unifying scattered opposition ranks next month: the idea is to forge an opposition that reflects the weight of groups fighting on the ground.
Meanwhile, attacks by Islamic State (IS) in Paris and its shooting downing of a Russian civilian airliner over Sinai have brought new focus to the other war raging in Syria: that against the jihadist group that controls swathes of the east.
Facing French and intensified Russian air strikes in response, Islamic State is on the backfoot. It has recently lost ground to U.S.-backed Kurdish and Arab forces, the Syrian army, and other rebels who are fighting both Assad and Islamic State.
The prospects of Assad's foreign friends and enemies joining forces in the fight against Islamic State in Syria appear dim, however. U.S. President Barack Obama said on Tuesday Russia was welcome to join the alliance against IS, but must redirect its air strikes away from rebels towards the jihadists. Russia says publicly it is attacking IS targets.
The fundamental divergence over whether Assad should be removed between the United States and Saudi Arabia on one hand, and Iran and Russia on the other, may well undo the Vienna process launched on Oct. 30. Its aims include a ceasefire and talks between the government and opposition leading to a new constitution and elections.
BATTLE FOR LATAKIA HILLS
"The political impact of the Russian escalation thus far is more significant than the actually military impact," said Noah Bonsey, senior analyst with International Crisis Group, in reference to the Vienna meeting.
"There isn't much reason to be optimistic about (Vienna's) potential to really make major headway towards resolving the conflict, but at least it has got everyone talking again. Most importantly it has given the opposition and its backers a reason to try to ... sort out the opposition's own internal equation, which is long overdue."
The conflict which spiraled out of an uprising against Assad's rule will soon enter its sixth year having killed about 250,000 people and driven more than half of Syrians from their homes. Refugees from the war have caused a crisis in Europe.
Militarily, the Russian-backed offensives have focused primarily in areas of western Syria crucial to Assad's survival and where Islamic State has little or no presence.
The most notable progress by the army and its allies against anti-Assad rebels has been in the northwestern province of Latakia and to the south of Aleppo, though rebels this week launched a counter-attack there. The army and its allies are trying to capture the main Damascus-Aleppo highway from rebels.
The government side has also recorded gains against Islamic State forces to the east of Aleppo, where it recaptured an air base, and in Homs province, where they have driven jihadists from villages seized recently by the group.
But in Hama, rebels equipped with plentiful supplies of TOW missiles have advanced at the government's expense, capturing a town on the north-south highway and managing to halt an attack in the strategically vital Ghab Plain.
"In the last two or three weeks, the Russian air strikes have started to show their results. This is apparent in southern Aleppo and Latakia," said Rami Abdulrahman, director of the Syrian Observatory for Human Rights, which tracks the war.
In rural Latakia region - where the Russian warplane was shot down - the army and its allies have recently seized several hill tops, endangering rebel control over surrounding areas, said a rebel with the Ahrar al-Sham group contacted by Reuters.
"The loss of hills has exposed vast areas which are under our control. It's the loss of these defensive outposts that have created a crisis for us," the rebel said. "The regime has made progress by heavy artillery bombardment and aerial bombing so their troops advance in territory that becomes open to them."
The Syrian military source said the results of the offensives to date included the destruction of rebel command and control structures and logistics. The pace of advances was not as important as securing captured territory, he said.
Yet rebels, working more closely together in response to the offensives, are striking a defiant and confident tone, buoyed by their success in Hama province. They view Assad's dependence on foreign allies as a sign of weakness.
"Everyone has the right to dream, and Putin dreams of eliminating the Syrian revolution. This is only a dream," said Jamil Saleh, head of a Free Syrian Army rebel group.
"The Russian intervention, while leaving more destruction, has raised morale and brought more unity in (rebel) ranks and this is positive," said Idris Raad, a senior figure in Failaq al-Sham, an Islamist insurgent group.
International Crisis Group's Bonsey said: "In terms of the regime's first priority - the war against the anti-IS opposition groups - it continues to be a mixed bag from the regime's perspective ... there's nothing we would characterize as fundamentally shifting the balance of power."
"Its scorecard against ISIS (IS) is looking a bit better."
(Writing by Tom Perry, editing by Peter Millership)