beirut syrian kurdish ypg militia say sunday fully capture deir al-zor eastern countryside islamic state help u.s.-led coalition russia ypg spearhead syrian democratic force sdf alliance mostly kurdish arab militias fight islamic state washington back sdf offensive deir al-zor province border iraq focus territory east euphrates river western bank syrian military wag attack islamic state support iran-backed militias russia separate assault advance opposite side river bisect oil-rich deir al-zor mostly stay way u.s.-led coalition russian military hold deconfliction meet prevent clash plan troop though two offensives sometimes come conflict sdf powerful component ypg announce defeat islamic state militants side cooperation arab tribes u.s.-led coalition russian force syria provide air logistical support advice coordination grind statement say hope increase support ensure necessary air cover ypg spokesman declare victory village deir al-zor presence russian envoy moscow hmeimim military base syria say u.s. defense secretary jim mattis say week battle islamic state enter final stag expect focus move toward hold territory instead arm syrian kurdish fighters washington support ypg infuriate turkey see grow influence kurdish force border security threat ankara consider ypg extension outlaw kurdistan workers party pkk movement fight decades-long insurgency turkish soil since start syria conflict 2011 ypg ally carve autonomous regions north control around quarter syria large part outside government control seize vast land islamic state autonomy plan face opposition battlefield ally washington turkey syrian government ypg say sunday form civil councils deir al-zor include kurds arabs components base principle democracy self-rule would mirror govern arrangements towns cities kurdish fighters ally capture islamic state close collapse syria syrian kurdish leaders hope phase negotiations shore autonomy north recent months damascus government iranian ally forcefully assert ambition take territory control kurdish-led force syrian kurdish ypg say seize eastern region islamic state