Across the north and east, the Islamic State of Iraq and the Levant (ISIL) has set up checkpoints on roads to border crossings, and opened fronts to crush other rebel groups fighting to oust President Bashar al-Assad.
Residents have told AFP of a strategy that involves ISIL taking over resources and routes using brutal methods aimed at forcing the population into submission.
Analysts and activists on the ground have also noted the tactic.
"ISIL has been acting in such a way as to aggressively assert itself within the complex multi-dimensional insurgent theatres in northern and eastern Syria," said Charles Lister of IHS Jane's Terrorism and Insurgency Centre.
Jihadists have even sought to justify the strategy on Internet forums by accusing Western-backed groups, including Ahfad al-Rasul and the Northern Storm brigade, of acting like the US-funded "Sahwa" who fought Al-Qaeda in Iraq.
But Lister said ISIL had adopted a "perceivable strategy of acquiring and consolidating control of areas on Syria's borders with both Iraq and Turkey", ever since it came on the scene in the late spring.
"This allows the group easy access to new recruits, sources of funding and supplies," he told AFP.
"It's by no means impossible that it intends to put a stranglehold on the ability of moderates (rebels) to secure sustainable levels of supplies from across the borders," Lister added.
Havidar, a Kurdish-Syrian activist and citizen journalist who has covered fighting between ISIL and Kurds, said ISIL's endgame was to establish an Islamic state.
"ISIL doesn't have an ideological problem with the Kurds or with anyone else. It just wants no other group to have any arms or self-sufficiency, to create a state that extends from northern Syria into Iraq," he told AFP.
Another activist in Raqa, near the Turkish border, said it was now virtually impossible to leave Syria without crossing through one of their checkpoints.
ISIL has a grip on Raqa, the only provincial capital in Syria that is completely out of Assad's control.