NEW : Guidance system failed , Iranian official said . Iran claimed to have shot down the drone . The RQ-170 Sentinel drone crashed in Iranian territory . In July , Iran 's military made a similar claim , saying it downed a U.S. `` spy drone '' flying near its Fordo nuclear enrichment plant in Qom province . The unmanned aircraft was part of a CIA training mission .
NEW : Guidance system failed , Iranian official said . Iran claimed to have shot down the drone . The RQ-170 Sentinel drone crashed in Iranian territory . The unmanned aircraft was part of a CIA training mission .