Britain and its Western allies have held their first face-to-face talks with Islamist factions fighting President Bashar al-Assad of Syria, including militant groups demanding a hardline sharia state, as the secular forces they previously backed lose ground.
The meeting was held in the Turkish capital, Ankara, officials said, as the Western alliance grows increasingly alarmed by the strength of jihadist factions linked to al-Qaeda that now dominate parts of rebel-held territory.
The Western alliance have previously refused to back several of these Islamist groups for fear that arms sent to moderate groups would end up in the hands of the extremists.
The officially recognised head of the Free Syrian Army, General Salim Idris, this week repeated his belief that if Assad falls from office, rebels will have to join forces with the remnants of his army to drive al-Qaeda forces out of Syria.
"Most of the rebels taking part were from the middle ground, but then moved down the spectrum," a Western official briefed about the talks said.
"The aim was to understand where these Islamic groups stand on the spectrum."
The most significant development on the ground has been the formation of a new pan-Islamist alliance among the rebels, confirmed at the end of November.
Some of the brigades that signed up were "moderate Islamist" groups that had previously been backed by Western allies, such as the Liwa al-Tawhid in Aleppo, and were loyal to Idris and the FSA's Supreme Military Council. But others included Ahrar al-Sham, a hardline Islamist group that has rejected the West and Idris and since last year fought alongside Jabhat al-Nusra, the al-Qaeda faction that signalled its presence in Syria last year with a series of suicide bombings.
Both groups contain foreign jihadis. Apart from the general rise of militant Islam, intelligence services fear that their growing role may feed back later into Islamist terrorism in Europe. As such, the decision to deal with this new alliance is sensitive and a reversal of previous hopes to rely only on pro-Western forces.
The new Islamist alliance is said to make up about half of the total rebel fighting force, if not more, with al-Qaeda groups comprising much of the rest.