Division 30 appears to have walked into a trap soon after its U.S.-trained contingent of 54 fighters entered Syria on July 12 to join up with fellow rebels at Azaz, just south of the Turkish border town of Kilis. Nearby were extremist fighters from Jabhat al-Nusra, the al-Qaeda affiliate in Syria, but commanders didn’t think Jabhat al-Nusra would attack. That expectation proved wrong.

The Jabhat al-Nusra extremists regarded Division 30 fighters as “American agents,” according to their Web postings. They kidnapped seven Division 30 fighters on July 29 and attacked its headquarters at Azaz on July 31. Jabhat al-Nusra kidnapped at least five more fighters a few days later. The United States launched airstrikes July 31, but they had little effect.

A Jabhat al-Nusra fighter named Ahamed Shaheed boasted online Thursday: “Just got a bran new M16 taken as ganimah [war spoils] from Division 30 haha,” according to monitoring by Site Intelligence Group.