Isis attacks have caused extensive damage to a Syrian airbase used by Russian forces, satellite imagery reveals.
Four helicopters, 20 lorries and a supply depot were destroyed in a series of fires at the T4 airbase, images acquired by the intelligence company Stratfor suggest.
The T4 base, also known as Tiyas, is located in Homs province near the city of Palmyra, and sits near a strategic crossroads leading to Deir ez-Zor, the Syrian capital of Damascus and Raqqa, the de facto capital of Isis.
The Isis news agency Amaq reported on the destruction at the air base on 14 May, releasing a statement to say: "4 Russian attack helicopters and 20 trucks loaded with rockets burn inside T4 Airbase, east of Homs, after a fire breaks out nearby."
The Stratfor report states: "Around the same time, loyalist forces reported that an accidental explosion had taken place in an ammunition storage area at the air base."
After analysing satellite imagery of the base, the US geopolitical intelligence think-tank concluded: "Ordnance impact points are visible, especially around the structurally reinforced aircraft shelter and the cargo truck marshalling area.
"The imagery strongly suggests that the explosions that destroyed approximately 20 vehicles and four Russian attack helicopters were not accidental but were related to Islamic State artillery fire."
Along with the four Russian Mi-24 Hind attack helicopters, the Stratfor report said a Syrian MiG-25 jet also appears to have been damaged.
A spokesman for Russia's Defence Ministry said reports of the destruction of Russian helicopters "were created by propagandists of [Isis]".
Major General Igor Konashenkov told the Russian news agency TASS: "[T]he rumours about the destruction of a group of Russian helicopters and two dozen trucks were created by the propagandists of [Isis] who unsuccessfully tried to ‘sell’ this alleged piece of news about ten days ago.
He added: "As for the photos of the Syrian airbase, the burnt aircraft and motor vehicles, as well as numerous craters created by reactive shell explosions have been present there for more than one month.
"This is the result of fierce fighting for this aerodrome between the Syrian government troops and militants of terrorist groupings."
However, Stratfor analyst Sim Tack told the BBC: "So what the imagery tells is that first of all this was not an accidental explosion. It shows very clearly that there were several different sources of explosions across the airport, and it shows that the Russians took quite a bad hit.
"An entire combat unit was wiped out - four helicopters total - as well as some damage to some of the Syrian planes on the airport, and also very notably a logistics depot, likely one that was being used to supply those specific combat helicopters.
He added: "The IS account that was released after the attack is very accurate. And it's also one of the reasons that leads us to belive this was indeed an IS attack rather than an accidental explosion, because that first statement shows the knowledge that the Islamic State had about what exactly was destroyed in the attack."
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