The loss of some territory in the Raqqa Province to Kurdish YPG forces had fueled reports that ISIS was on the defensive in Syria, and not doing particularly well. The group seems to have decided, instead of confronting the YPG advance head-on to move against major Kurdish targets in a counteroffensive.
The battle of Kobani, which ISIS lost five months ago, was seen as a major turning point for Kurdish forces, but ISIS has returned today, with fighters disguised as Kurdish forces infiltrating the city and carrying out a series of attacks that left at least 35, and potentially many more, killed.
This was just half of the ISIS counteroffensive, however, with forces moving west against Kobani but also moving east in a new assault on Hasakeh, the de facto capital of Syrian Kurdistan. The city is being protected by both YPG forces and the Syrian military, but ISIS reported has seized a district in the area.
Though this is something of a change in tactics in Syria, it is also the first time ISIS has lost any meaningful territory in Syria, and actually reflects quite closely with their tactics against Kurdish Peshmerga forces in Iraq, where they regularly respond to the loss of territory by seizing other territory elsewhere in counter-strikes, forcing the Peshmerga to spread itself thin along a growing frontier.
Since the Arab town seized in Raqqa Province is much less important to Kurdish forces than Kobani or Hasakeh, expect the ISIS moves to force the YPG to back off and focus on defending their more important sites, potentially weakening their foothold in Raqqa and allowing ISIS to take it back in the future.