The statement released Saturday said the remains were found Friday on the Nuevo Ojo de Agua ranch in an area frequently used by Central American migrants traveling north. The statement said there were no visible signs of violence on the remains, which "break easily."
The statement said authorities will "not discard any line of investigation."
The remains were discovered stacked atop each other in the cave, said a prosecutor's office employee who was not authorized to release information and asked not to be identified. The remains have been moved to the state capital of Tuxtla Gutierrez for examination, the employee said.
Mass graves have been found in the past two years mainly in northern Mexico containing the bodies of dozens of migrants and others allegedly killed by drug cartels.