Desertions and deaths on the battlefield have left ISIS with 20 per cent fewer fighters in the Middle East in just the last year, a US intelligence report has found.
American officials believe the extremist organisation has between 19,000 and 25,000 terrorists in Iraq and Syria, compared to 2014 estimates of 20,000 - 31,000 fighters.
However, the size of the terrorists ranks in Libya has doubled over the same period, from around 3,000 to 6,000, as the group establishes a new base on Europe's doorstep.
Fighters deserting the depraved group and a high death toll thanks to Russian bombing raids are thought to be behind the shrinking terror army.
The White House said the report, released last week, showed the campaign to crush ISIS - which has been aided by RAF jets - was making progress.
Spokesman Josh Earnest said: "ISIS has sustained significant casualties" and that the new intelligence estimate "means they continue to be a substantial threat, but the potential numbers have declined".
The figures also suggest international efforts are beginning to stem the flow of foreigners seeking to join the movement, Express reported.
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