Dozens of Russian military vehicles and attack helicopters deployed to Syria may have have been destroyed in an apparent attack by Isil.

Images released on Tuesday by Stratfor, the American intelligence think tank, show what appear to be the blackened remains of four attack helicopters and dozens of lorries at an airbase used by Russia near the town of Tiyas.

The images appear to confirm an earlier claim by so-called Islamic State of Iraq and the Levant (Isil) that four helicopters and 20 lorries had been destroyed in a fire at the base.

That would represent Russia's worst losses in terms of materiel since Vladimir Putin ordered intervention in Syria in September.

Russia dismissed the Isil claim as “propaganda”, said said the images showed damaged inflicted during months of heavy fighting for the base before Russian forces occupied it earlier this year.