Dozens of people have died in an offensive by so - called Islamic State on government - held areas of Deir al - Zour in eastern Syria, local media say. The Syrian Observatory for Human Rights said 85 civilians were killed in the attack, as well as 50 Syrian soldiers. Syria's state news agency Sana reported that around 300 civilians had died in the Baghaliyeh area of the city. Meanwhile, the UN warned of "sharply deteriorating conditions" in the besieged areas. Around 200,000 people were in these areas, the UN Office for the Coordination of Humanitarian Affairs (OCHA) said. The IS assault on government-held areas in the city began at dawn on Saturday, Syria's Local Coordination Committees (LCC) said. A car bomb explosion was followed by a ground attack, the LCC said. Government forces retaliated with air strikes and heavy artillery, the report said. Russia said it had dropped aid to civilians caught up in the siege. There have also been reports of Russian airstrikes in the vicinity.