An attack by Islamic State on the eastern Syrian city of Deir Ezzor has left at least 85 civilians and 50 government troops dead, a monitoring group said, with state media denouncing a "massacre", The Guardian reported.
Syria's state news agency Sana, quoting residents, said as many as "300 civilians" were killed in the onslaught.
If confirmed it would be one of the highest tolls for a single day in Syria's nearly five-year war.
The bloodshed in Deir Ezzor came as regime forces battled Isis in the northern province of Aleppo, killing at least 16 jihadists, and as airstrikes hit the Isis stronghold of Raqqa.