Isis grad rocket attacks linked to destroyed Russian attack helicopters at Syrian T4 airbase

A grad rocket assault shown in Islamic State (Isis) propaganda has been linked to the destruction of four Russian attack helicopters and 20 lorries at the joint Syrian and Russian T4 Airbase.

Satellite imagery uncovered by the private intelligence company Stratfor, and relayed to the BBC, has shown that fires inside the base, roughly 40 miles (60 km) from Palmyra, had destroyed the Russian military hardware.

The cause of the fire has not been definitively confirmed. One Russian website reported that a large fire in one section of the base spread to the 20 vehicles and then destroyed the helicopters after a nearby fire tank exploded.

However, experts have said the blaze could have been caused by an Isis (Daesh) attack, published by the militant group's Amaq agency. Isis first released pictures of its fighters firing grad missiles online but did not claim responsibilty for the destruction at the base.

Stratfor has said that its satellite images show the explosions were not an accident "What the imagery tells us is that first of all this was not an accidental explosion, as some of the rumours kept saying," Stratfor military analyst Sim Tak told the BBC.

"It shows very clearly that there are several different sources of explosions across the airport, and it shows that the Russians took a quite a bad hit.

Tak explained that Isis reports were "very accurate" but he could not account for why the group had not claimed responsibility for the later destruction.