ISIL is reportedly moving fighters and family members out of its self-declared capital, Raqqa, as an intensified air campaign by coalition forces begins to bite.
Militants in ISIL's so-called caliphate across Syria and Iraq have faced several setbacks over the past week, Kurdish forces splitting a key cross-border supply line, and a US-led military coalition targeting its oil smuggling network and killing dozens of militants.
The Syrian Observatory for Human Rights, a monitoring group, said yesterday that Isil had started moving the family members of foreign fighters across the border to Mosul, apparently claiming that Raqqa was no longer safe.
David Thomson, a journalist who monitors French nationals fighting in Syria, said French jihadists had begun to leave the city in the days before the group's attacks in Paris, citing Isil sources.
Isil maintains a tight stranglehold over the flow of information outside of territory it controls, and it was not possible to immediately verify the claims of movements to Mosul, a city that is regularly bombed by coalition forces.
France launched a third night of retaliatory strikes on Raqqa on Tuesday night, reportedly hitting two command centres. At least 33 militants have been killed in the city and its outskirts over the past three days, according to the Syrian Observatory.
Local activists say the increased bombardment, including last week's assassination of the executioner known as Jihadi John, has spread fear and paranoia through the militants' ranks. "It's really affecting people, they are getting worried," said Abu Ibrahim al-Raqqawi, a spokesman for Raqqa is Being Slaughtered Silently, a group of anonymous media activists who risk their lives to smuggle information out of the city.
"If they are gathered together, the fighters will scatter in all directions when a drone or a war plane is seen overhead. They hide among the people, they run into houses," he said.
Isil is facing pressure across its so-called caliphate, after Kurdish and Yazidi forces recaptured the town of Sinjar last week in a two-day operation which faced little resistance. They are also being squeezed in northeastern Syria where a western-backed coalition of Kurdish and Arab forces are closing in on Isil-held territory.
The terror group is now understood to be retrenching operations, moving heavy weaponry and oil supplies to Deir Ezzor, another Syrian stronghold.
"Heavy weaponry, oil facilities and the headquarters belonging to the group... have been relocated to Deir Ezzor using troop carriers and tank transporters," reported Deir Ezzor 24, an independent news outlet. The process was being carried out in stages to avoid coalition airstrikes.
On Monday, US jets attacked hundreds of oil smuggling trucks in Deir Ezzor that Isil had been using to smuggle the crude oil it has been producing.
Estimates by local traders and engineers put crude production in Isil-held territory at about 34,000-40,000 barrels-per-day, bringing in a profit believed to be around pounds 1million a day.
Although the US-led coalition has often bombed oil production sites, it had previously refrained from striking tankers due to internal disputes over whether their drivers should be classed as civilians.