The spectre is looming of a second Syrian civil war, with the head of the opposition's official forces declaring that he is prepared to join regime troops in future to drive out al-Qaeda-linked extremists who have taken over swathes of rebel-held territories.
General Salim Idris, the commander of the Free Syrian Army, warned that in particular Isis (Islamic State of Iraq and al-Sham), with thousands of foreign fighters in its ranks, was very dangerous for the future of Syria and needs to be confronted before it becomes even more powerful.
Western security agencies now believe Syria poses the most potent threat of terrorism in Europe and the US, from where hundreds of Muslims have gone to join the Syrian jihad. MI5 and Scotland Yard's anti-terrorist branch recently tackled the first case of men sent from there specifically to carry out attacks in London.
One senior Western intelligence official stressed the Syrian regime's forces must be preserved for the battles ahead against the Islamists and the need to avoid the mistakes made in Iraq and Libya, where the army and police were disbanded with the fall of Saddam Hussein and Muammar Gaddafi, allowing terrorist groups to rise in a security vacuum.
The official held that talks between the regime and rebels, set to take place in Geneva in January, could be the beginning of an anti-al-Qaeda front in Syria, with a negotiated settlement to end the conflict.
Speaking in Istanbul, Idris, a former officer in the regime's army, said he and his associates were dropping the precondition that Bashar al-Assad must leave power before the Geneva meeting. Instead they would be satisfied if his departure were to take place at the end of the negotiation when Idris will join forces with the remainder of the regime to mount an offensive against the Islamists.
However, the opposition would like to see evidence of good faith from the regime, which would include allowing supplies to get to communities trapped by the fighting.
Idris complained his men were having to fight a war on two fronts: against al-Qaeda at 24 different locations in the last six months while at the same time pounded by Assad.
What is left of the moderate opposition forces are bitterly critical of Western powers for encouraging people to rise up against the regime, but then doing little to help. Meanwhile, Isis and another Islamist group, Jabhat al-Nusra, have grown in numbers and influence due to money and arms from Qatar, Saudi Arabia and other Gulf states.
The jihadists have been occupying areas in the provinces of Aleppo and Idlib with moderate fighters being killed or forced to flee.
The FSA has now produced an intelligence dossier that estimates Isis alone now has 5500 foreign fighters as well as 2000 indoctrinated Syrians in the north, with 15,000 others who provide support to the group.
The most dangerous and barbaric of the foreign fighters are 250 Chechens, who are fitted with explosive vests when they reach Syria.
Isis employs the policy of kidnapping, its prison now holding more than 35 foreign journalists as well as 60 political activists, and more than 100 FSA members.