CHIHUAHUA, Mexico (AP) _ Mexico's army has begun investigating 570 soldiers based in the border state of Chihuahua after troops apparently burned flour instead of cocaine during a ceremony last week, news reports Friday said.

Gen. Juan Morales Fuentes, commander of the 5th Military Zone, said flour instead of about 12 pounds of cocaine was burned at the Oct. 22 event. The ceremony was watched by schoolchildren and officials from the federal attorney general's office, according to El Diario de Chihuahua and Reforma of Mexico City.

El Diario reported Thursday that all 570 members of the 96th Infantry Battalion had been confined to barracks. The battalion has been working in anti-narcotics efforts along the U.S. border from western New Mexico to the Big Bend area of Texas.

Mexico's military has taken a major role in drug interdiction in recent years.

Reforma quoted Morales Fuentes as saying half the men were being drug tested. El Diario said all would be.

Reforma quoted the general as saying that not all of the cocaine had been stolen.