beirut syrian observatory human right say islamic state attack thursday cut main road deir al-zor city palmyra syrian military source deny observatory britain-based war monitor say islamic state seize town al-shoula road syrian troop ally battle around heavy air cover syrian military source say army thwart attack deny islamic state fighters take town cut route militants try mount attack territory control southeast deir al-zor city near border iraq source add receive blow succeed source say road army ally seize recent weeks serve major supply route government territory eastern city russian air power iran-backed militias syrian army reach deir al-zor city last month break islamic state siege enclave last three years towns along euphrates river downstream city fast become last major footholds syria focus multi-sided war islamic state militants back foot iraq syria lose vast territory different enemies year u.s.-led jet special force alliance kurdish arab militias also battle islamic state river eastern bank separate offensives advance race capture swathe deir al-zor province media unit amaq say thursday militants take al-shoula nearby village wag attack include suicide bombers capture two russian force russian defense ministry deny military personnel take hostage ria news agency say cite russian military official hmeimim air base syria incidents capture lose russian servicemen deir al-zor province syrian provinces official say islamic state leader abu bakr al-baghdadi exhort followers thursday stand fast keep fight first purport audio communication almost year syrian observatory say cut deir al-zor road military source deny