Heavy clashes between the Syrian Arab Army (SAA) and ISIS had taken place in the western Deir Ezzor countryside, the Syrian Observatory for Human Rights reported on August 27.
The SAA, backed by the National Defense Forces (NDF) and Liwa al-Quds, launched a combing operation in the region earlier this week. ISIS remnants are the main target of the operation.
A day earlier, the SOHR reported that a joint group of the NDF and Liwa al-Quds was lost in the desert of al-Mayadin city while taking part in the operation.
The London-based monitoring group said contact was lost with a second unit, consisting of NDF fighters and their commander, on August 27.
Communication failure and errors in navigation were likely behind the disappearance of the two groups. However, ISIS terrorists may be also responsible.
ISIS cells have been very active in western Deir Ezzor. The terrorists are sneaking into the region from their strongholds in the nearby Homs desert. U.S.-backed fighters in al-Tanaf garrison are arming and supplying the terrorists, according to several reports.