And Turkey is one of the rebels staunchest backers.

Via LA Times:

Prosecutors in southern Turkey have alleged that Syrian rebel groups were seeking to buy materials that could be used to produce highly toxic sarin gas, Turkish media reported Friday.

An indictment issued in the southern city of Adana alleged that a Syrian national identified as Hytham Qassap, 35, was in Turkey trying to procure chemical materials for a pair of well-known Islamist rebel blocs, Al Nusra Front and the Ahrar al-Sham Brigades, the reports said. Washington has designated Al Nusra Front as a terrorist group linked to Al Qaeda.

Neither group is affiliated with the U.S.-backed Free Syrian Army.

Five other suspects, all Turkish citizens, were indicted in the case, Turkish media reported. All six suspects have pleaded not guilty, according to the English-language Hurriyet Daily News, which quoted from the indictment.

The alleged ring never manufactured sarin, a potent nerve agent, according to Turkish media.

The investigation began with a tip to police that some Syrian rebel groups might be seeking to obtain materials in Turkey to produce chemical weapons, the reports said. In May, Turkish police arrested 11 suspects in connection with the case. Turkish officials denied as erroneous some initial reports that sarin had been seized as part of the investigation.