Mohannad Ahmed al-Tallaa, the commander of the rebel battalion stationed at Tanf, said they began working with US troops at the base late last year. A former officer in an elite Syrian army unit, he defected early in the civil war and has been a vital player in the rebel fight in Deir Ezzor, a province in eastern Syrian that has become a major ISIS stronghold. He created the battalion, called Maghaweir Al-Thowra, or Commandos of the Revolution, with the aim of working with the US-backed coalition to free Deir Ezzor from ISIS, he said, adding that he and his men now live with their US partners. “I’m sitting with them right now,” he said when reached by phone on Tuesday night; men with American accents could be heard speaking English in the background.