ISIS released a video on Wednesday showing a Syrian teenager being executed with an RPG in Deir el Zor.
The purported video claims Ibrahim Alsharidah from Sheitat tribe was killed by Lavdrim Muhaxheri, an Albanian ISIS militant wanted by Interpol.
ISIS had killed around 900 al Sheitat tribe members in 2014 and thrown in mass graves, after they attempted a rebellion against ISIS.
ISIS executed 700 of al Sheitat tribe members, most of them by beheading, in only two weeks in last August. The majority of them were civilians according to Reuters.
The conflict between ISIS and Sheitat, who are about 70,000 people, flared after the militants took over two oil fields in July 2014.
According to reports, eight members of the al Sheitat tribe were killed in the recently captured city of Palmyra.
ISIS began approaching Palmyra on May 13. The ancient city has a strategic importance for ISIS as it provides the possibility of using their position there to cut the supply lines of the regime forces stationed in Deir el-Zor and also to secure their own supply lines to their fighters in the Qalamoun Mountains and Eastern Ghouta in rural Damascus, as well as those approaching the outskirts of the city of Homs.
According to Syrian state television, pro-government forces withdrew Wednesday night after evacuating the majority of the population.