MEXICO CITY (AP) _ A police helicopter on a drug-eradication mission crashed in southern Guerrero state, killing the craft's two-man police crew and nine soldiers, authorities said Sunday.

The federal attorney general's office said the Bell 212 helicopter went down Saturday after developing mechanical failure, but did not elaborate further.

Army and police teams were investigating the cause of the crash, which occurred near the state capital of Chilpancingo, 130 miles south of Mexico City.

Guerrero state has been wracked in recent weeks by gunfights between the army and leftist rebels, and the state is also believed to be one of the largest drug-producing areas in Mexico.

In the past, the army and police have engaged rebels in combat while on what were purportedly routine anti-drug missions.

The newspaper La Jornada, citing sources it did not identify, reported that the chopper might have been carrying troops to the scene of a 1995 police massacre of 17 farmworkers, to lay a trap for leftist rebels expected to commemorate Sunday's third anniversary of the killings.