Confrontation between rebels and al-Qaeda extremists in Syria has revealed the limitations of Bashar al-Assad's armed forces, which have belatedly moved to exploit the infighting, but only at the cost of giving up territory in other parts of the country.
In recent days Mr Assad's forces have retaken a hilly area in Aleppo that was long under rebel control, putting them in a position to retake a strategic area on the outskirts of the city, Syria's largest.
But in redeploying forces in Aleppo, the regime has had to give up control of the southern city of Jassem and the long-contested Ghouta neighbourhood east of the capital, Damascus. It has also all but suspended the fight for Qalamoun, a strategic area between the capital and the Lebanese border, say watchers of the shifting battle lines.
The rise of extremist Islamist groups such as the Islamic State of Iraq and the Levant, or Isis, within the rebel camp has raised doubts about the armed opposition, while an assault on the group by other rebel organisations has clouded political and military battle lines."This is one of the most important problems that the regime is facing," said Emile Hokayem, an analyst at the International Institute for Strategic Studies. "It can't deploy its conventional forces everywhere at the same time."
The complexity of Syria's war has muddied the goals and agenda of an international conference on the country's future to be held in the Swiss town of Montreux next week.
Western officials have in recent months engaged with Mr Assad's government in an attempt to remove chemical weapons stockpiles from the country and, according to some reports, to get information about extremist groups, while at the same time providing material backing and political support to some of the groups fighting the regime.
Even with the rebels in turmoil, the conflict remains largely in a stalemate; fronts have barely shifted over the past year despite predictions of imminent regime victories and the influx of reinforcements in the form of Lebanese, Iraqi and Iranian fighters and advisers.
Close observers say the Assad regime proved slow to take advantage of the outbreak of rebel infighting – although the factions have depleted their own ranks effectively: more than 700 rebels have died in factional fighting since January 3. "Only when the fighting appears to slow will the government feel the need to push with its full strength," said Charles Lister, a Syria expert at the Brookings Doha Centre.
Still, both Isis and other rebel umbrella groups, such as the newly formed Mujahedin Army and the Islamic Coalition, have proven adept at holding off the regime while simultaneously fighting each other. Isis has managed to retake control of the northern city of Raqqa from rival rebel groups while attacking a nearby critical regime military base. In Aleppo, other rebel factions have managed to fight Isis while defending the area of Sheikh Najjar, a crossroads that is crucial to linking rebel-controlled areas in the north.
In Aleppo, Mr Assad's forces have managed to take over Naqareen, a hilly area overlooking Sheikh Najjar, redeploying 3,000 men in preparation for a push to retake the strategic crossroads."There is no doubt Assad has sought to exploit the infighting but the gains aren't very substantial," said Aymenn al-Tamimi, an Oxford researcher and fellow at the Middle East Forum, a think-tank. "Even with the infighting, he wasn't able to defeat the rebels."
"The regime is preparing the area for a battle," said Cedric Labrousse, a researcher at Rennes university in France who has been mapping rebel and regime advances and losses. "If the rebels lose the Sheikh Najjar industrial area, the regime cuts roads to the northern countryside."
But Mr Labrousse and others say the regime's redeployment has created other opportunities for rebels, perpetuating the stalemate. "The rebellion can advance itself in Damascus because the regime is concentrating its forces in Aleppo," he said.
Still, the opposition has been unable to use any gains to break the overall deadlock. "Even when the rebels are able to push back, they are not able to consolidate," said Mr Hokayem. "This has to do with the lack of supplies and co-ordination."Where there has been no rebel infighting, such as in the southern town of Jassem in Deraa province, or Ghouta in the eastern suburbs of Damascus, the opposition forces have made advances, especially where fragmented rebel factions have united under the banner of Jabhat Al-Nusra, a hardline, highly effective Islamist rebel group supported by wealthy donors in the Arabian peninsula.
The regime, too, has been stymied in its efforts to turn tactical gains into game-changing strategic advances. Its conventional forces aren't robust enough to fight on multiple fronts. It has settled on a strategy of aerial and artillery bombardment of rebel territories and using irregular militias, including Lebanese Hizbollah fighters and Iraqi Shia militias, to hold territory won by its conventional armed forces.
"Government forces have consistently suffered from an inability to maintain simultaneous and concerted military operations across multiple theatres of the country for long periods of time," said Mr Lister.