A 26 May Islamic State attack on rebel territory led to the successful capture of multiple northern Aleppo villages, including the strategic towns of Kafr Kalbin and Kaljibrin. These two towns are on the Azaz-Mare' road, and their capture resulted in the cutting in two of the Azaz pocket. In order to more effectively defend the now isolated town of Mare', rebel forces handed over Sheikh Issa, the town to the west, to the Syrian Democratic Forces. Thousands of civilians, including residents of IDP camps, have fled either to the territory immediately surrounding Azaz, or into PYD-run Efrin Canton. They have not been allowed into the town itself, due to fear of IS sleeper cells, who appear to have played a significant role in the recent offensive.
Islamic State media has published photos and videos of the weapons and equipment they've siezed from multiple rebel groups, including those categorized as "Vetted Syrian Opposition," such as Jaysh al-Mujahideen and Division 13. They specifically show a captured crate of artillery shells bought by Saudi Arabia from Bulgarian company Aheloy-opm. Islamic State media has also highlighted the presence of American A-10s operating in the area.
Rebel fighters have since recaptured Kaljibrin, but their attacks on Kafr Kalbin have been defeated. Islamic State attacks on Mare' have continued. Almost all civilians within the town have fled into Efrin Canton, some heading to Azaz.