ISIS militants massacred 175 workers who were captured at a cement factory Northeast of Damascus, a Syrian military source said on Friday.
No further details were provided on the nature of the killings.
It was reported that Islamic State fighters kidnapped scores of workers in an area northeast of Damascus after launching an attack on government forces there this week, Syrian state television and a monitoring group said on Thursday.
State TV quoted the industry ministry as saying 300 workers and contractors of Al Badia Cement were taken from near the town of Dumeir and that the company had lost all contact with them.
The British-based Syrian Observatory for Human Rights later gave a figure of around 170 workers who had been abducted from the cement factory and taken to undisclosed areas controlled by the militants in the Damascus suburbs.
The monitor, which tracks violence across the country, said 140 workers at the plant had fled before the militants arrived.