The state-run SANA news agency said that most of those killed in yesterday's attacks were elderly people, women and children while opposition activists said many of the victims were Syrian soldiers and pro-government militiamen and their families.
The killings are some of the worst carried out by the extremist group, which controls large parts of Syria and Iraq and has killed thousands of people in both countries.
It added that many of them were shot dead or beheaded.
The Islamic State group controls most of Deir el-Zour province and much of the capital with the same name, while the government controls several districts in the northern part of the city and the adjacent military airport.
Also Read
Most of the casualties took place in the area of Baghaliyeh near the city.
The reports could not be independently confirmed.
The IS-affiliated Aamaq news agency had reported a large- scale multi-pronged attack on Deir el-Zour that began with a suicide bombing.
Today, it reported that the group expanded its control of areas west and northwest of Deir el-Zour, adding that around 110 Syrian government forces were killed and at least five others captured.