beirut u.s.-backed militias say capture syria large oil field sunday press assault islamic state east country syrian democratic force sdf say take al-omar field eastern bank euphrates river early hours force manage liberate field without notable damage say lilwa al-abdallah spokeswoman offensive deir al-zor province jihadists hole build nearby district sdf try hunt say u.s.-led jet special force sdf battle deir al-zor border iraq alliance kurdish arab militias focus territory east river bisect oil-rich province syrian army russian air power iran-backed militias wag separate offensive islamic state mostly west river u.s.-led coalition russian military hold deconfliction meet prevent clash plan troop though two offensives sometimes come conflict islamic state lose vast territory across syria come attack last footholds strip euphrates valley desert deir al-zor sdf declare victory jihadists former headquarter raqqa city week sdf fighters would move frontlines deir al-zor speed battle eastern syria last month kurdish-led militias capture major natural gas field upstream sunday advance al-omar oil field lie 10 km 6.21 miles north town al-mayadin government troop ally take early month town turn major base islamic state militants u.s.-backed offensive drive raqqa syrian observatory human right say islamic state fighters withdraw oil field mount counter-attack overnight government force militants make gain around al-mayadin britain-based monitor say syrian military source deny say significant attack fight rag pace attack islamic state militants desperate attempt source say syrian arab army attack hit daesh position ... advance source say use arabic acronym islamic state u.s.-backed militias seize key oil field east syria sdf