washington/amman pentagon-backed rebel group u.s.-led coalition fight islamic state kill 20 islamic state fighters detain number militants southern syrian desert near base coalition say thursday statement coalition say maghawir al thawra rebel group coalition detect convoy near at-tanf near syrian border jordan iraq early wednesday carry operation prevent incursion despite presence russian-backed pro-syrian regime force area daesh still find ways move freely regime line pose threat brigadier general jonathan braga director operation coalition say use arabic acronym islamic state u.s. official speak condition anonymity say convoy come within establish 55 km 34 miles around tanf base u.s. special force operate another u.s. official say dozen militants capture rebel group statement add islamic state militants move freely areas control pro-syrian regime force second time month small group convoy daesh move eastern areas syria toward southern area areas control regime russians shi ite militias colonel muhanad al talaa commander maghawir al thawra tell reuters daesh convoy move regime russians see matter strange talaa say 20 islamic state militants kill syria u.s.-led coalition