A Mexican military helicopter has crashed in the Pacific coast state of Guerrero, killing an air force sergeant and seriously injuring two soldiers.

The Defense Department blames a mechanical problem for Wednesday's accident.

The Bell 212 helicopter was transporting an army officer and nine soldiers when it went down in a rural area in mountains known to be frequented by drug and criminal gangs.

U.S. officials recently delivered five Bell helicopters of a different model to Mexico as part of the "Merida Initiative" for aiding the Mexican campaign to curb drug traficking.