(CNN) -- Authorities in the Mexican state of Chihuahua continued Monday to investigate the discovery of a mass grave holding 18 bodies.
Carlos Gonzalez, spokesman for the Chihuahua state attorney general's office, confirmed details of the discovery.
It was not immediately know how long the bodies, which were discovered on Friday, had been buried.
The discovery was made after the Mexican military spoke with five men detained for marijuana possession. The men were in possession of 176 kilos (about 387 pounds) of marijuana, authorities said.
In the process of the interrogation the army was informed about possible "narco graves" on a ranch in Capricho, about eight kilometers (nearly five miles) south of Palomas, which is across the border from Columbus, New Mexico.
The military informed the federal attorney general's office, which was being assisted at the scene by forensic investigators and the Chihuahua state attorney general's office.
Authorities were working Monday to determine identities of the bodies and causes of the deaths.