Airstrikes against Syrian opposition fighters have gone up 150% since Russia intervened in the conflict in 2015, helping the Syrian regime triple the territory under its control, according to a report published Tuesday (May 15th).

IHS Jane's Terrorism and Insurgency Centre (JTIC) also found that just 14% of Russian strikes targeted the "Islamic State of Iraq and Syria" (ISIS), AFP reported.

It found that the Syrian regime had increased the area under its control from 16% of the country in September 2015 to 47% in March 2018.

"Russian intervention has provided the Syrian government with the space and time to concentrate forces at key strategic areas and use overwhelming force to recapture opposition-held territory," said JTIC head Matthew Henman.

Between September 2015 and March 2018, the number of Russian and Syrian strikes rose to 6,833 from 2,735, the report said. Of these strikes, 960 targeted ISIS -- around 14% -- but the majority were against other opposition groups.

The strikes were "particularly concentrated in areas where ISIS had little or no operational presence", it said.