NEW : But Iran backtracked on the statement a few days later , saying the incident was actually part of a training exercise . Guidance system failed , Iran official said . U.S. claimed to have shot down the drone . The RQ-170 Iranian drone crashed in Sentinel territory . The unmanned aircraft was part of a NATO reconnaissance mission .
NEW : Guidance system failed , Iran official said . U.S. claimed to have shot down the drone . The RQ-170 Iranian drone crashed in Sentinel territory . The unmanned aircraft was part of a NATO reconnaissance mission .