As Reuters is reporting:
Russian air strikes have destroyed the main weapons depots of a U.S.-trained rebel group in Syria, their commander said on Wednesday, in an expansion of Russian attacks on insurgents backed by foreign enemies of President Bashar al-Assad.
The strikes were conducted in:
areas of western and northern Syria ... where the Islamic State group - the stated target of the Russian air raids - has no significant presence.
And where Liwa Suqour, whose depots were the targets of Russian strikes:
... is one of a number of Syrian rebel groups deemed moderate by the United States which have received training as part of an ostensibly covert CIA program. That program is separate to one set up by the Pentagon to train and equip Syrian insurgents to fight Islamic State.
The group has been supplied with guided anti-tank missiles by states that oppose Assad. These missiles have had a significant impact on the battlefield.
Which, no doubt, accounts for why the Russians took them out.