Where have the ardent jihadists of ISIS gone after the fall of their self-proclaimed capital of Raqqa in Syria?
The city was the centre of the ISIS caliphate – a kingdom stretching across the northern territories of Syria and Iraq with a population of 10 million.
But since the caliphate was announced in 2014, ISIS has been pummelled by air strikes led by the USA and UK, while mainly Kurdish land forces have quickly regained lost ground, including the city of Mosul in Iraq.
As ISIS flags were lowered and the fighting ended, some ISIS faithful are corralled in a narrow strip of desert straddling the Syria and Iraqi border.
But the group seems leaderless and left mainly foreign fighters to battle over the fall of Raqqa.
Where the fighters have gone
Research by the Soufan Centre says thousands of fighters have packed their bags and secretly returned home.
The data says hundreds of fighters have been tracked.
Turkey had the largest contingent with 900 fighters. Another 800 have returned to Tunisia and 760 to Saudi Arabia.
The report also says 425 of the 850 British jihadists have travelled to the UK – around 100 are women and 50 children.
Richard Barrett, the author of the report, modafprovig.com said: “As the so-called Islamic State loses territorial control of its caliphate, there is little doubt that the group or something similar will survive the worldwide campaign against it so long as the conditions that promoted its growth remain.
“Its appeal will outlast its demise, and while it will be hard to assess the specific threat posed by foreign fighters and returnees, they will present a challenge to many countries for years to come.”
In his report, Barrett claims 5,600 former ISIS members have returned to 33 countries.
The worry is security forces do not have the resources to monitor the activities of such large numbers of jihadists crossing their borders and setting up home.
No one knows if they will continue to plot terrorist outrages or try to lie low to avoid detection and arrest.
“States have not found a way to address the problem of returnees,” said Barrett. “Most are imprisoned, or disappear from view. There will be a need for more research and information sharing to develop effective strategies to assess and address the threat.”