At the risk of undermining my previous reply, I offer the following link and excerpt:
To the east of Jarabulus flows the Euphrates River, beyond which the territory is controlled by Syrian Kurds, who carry out periodic raids on Jarabulus. On October 25, 2015, Turkish border guards fired upon Kurds crossing the river in boats. The Kurds accused the Turkish side of supporting ISIL.
A few days prior, Ankara had warned that any Russian aerial support for Syrian Kurds “will have serious consequences” (the Kurds themselves had already endorsed Russian actions in Syria and proposed opening a diplomatic mission in Moscow). “With Russian support, they are trying to seize the land between Jarabulus and Azaz, moving to the west of the Euphrates. We will never allow this,” said a Reuters source in Turkey.
The Kurds are trying to take Jarabulus to cut off the route of new recruits joining ISIL. The town is within a few hundred meters of the Turkish border, which is practically unmanned. The boundary between Syria and Turkey stretches out over more than 500 kilometers. Government forces control part of the Syrian territory along this border, and the Kurds control another part. ISIL holds about 100 kilometers, from Azaz to Jarabulus.
Along with the Turkish city of Karkamış, practically all foreign fighters joining the jihad on ISIL territory in recent years have passed through this area.
I thought this was such a good article that I checked the "About" section. It turns out that Meduza is a Russian media source. If it is propaganda it is very good propaganda.
I wonder how well ISIS can survive over time if they cannot get foreign fighters to replace the fighters killed through attrition, and the number of ISIS members dwindles?
Of course, ISIS can recruit fighters locally through conscription or volunteers, but these may not have the quality or motivation. Many if not a majority of the vehicle borne explosives used to blow up checkpoints so that ISIS fighters following behind can drive through, are reportedly driven by foreign suicide bombers, not locals. But ISIS can get fighters through the Libyan route, and when regular entrances into Syria are blocked by the Kurds (assuming they take and hold that last hundred kilometers of border), perhaps foreign fighters will turn to irregular border crossings, just as refugees seeking to enter Turkey from Syria have done? Though if foreign fighters seeking to enter Syria from Turkey must be guided through minefields as the article suggests, that may complicate matters.