beirut air strike carry unidentified warplane kill seven hezbollah fighters eastern syria three source familiar incident tell reuters monday identity warplane confirm source rule possibility russian friendly fire source say air strike happen air strike strike hezbollah position eastern homs province iran-backed lebanese group fight islamic state alongside syrian russian militaries ask report u.s. drone carry strike spokesman u.s.-led coalition say location outside area operations coalition also conduct air strike syria islamic state support syrian democratic force alliance arab kurdish militias air strike kill seven hezbollah fighters syria-sources