beirut syria army ally encircle islamic state city al-mayadin southeast deir al-zor eastern syria syrian military source say sunday al-mayadin one last strongholds islamic state fall back upon fertile area downstream deir al-zor euphrates valley launch counter attack central desert lose swathe territory year units arm force ally force continue advance number front ax deir al-zor countryside ... encircle daesh terrorists city al-mayadin military source say army ally reach deir al-zor september months-long offensive across syria desert recent weeks push euphrates towards al-mayadin however counter attack islamic state central desert region put pressure main supply road deir al-zor western syria syrian president bashar al-assad back war russia iran shi ite militias include lebanon hezbollah campaign islamic state mostly west bank river u.s.-led coalition also support rival campaign jihadists mostly east bank close recapture raqqa also advance downstream hold areas opposite deir al-zor u.s. officials previously say islamic state relocate diminish command propaganda structure al-mayadin force territory elsewhere syrian army encircle al-mayadin syrian military source