A draft report by a special prosecutor in Mexico accuses the military of killing hundreds of people in a counter-insurgency campaign that began in the 1960s.
A U.S. research group, The National Security Archive released a leaked copy of the report, which Mexican officials have not yet made public.
The draft report blames Mexico's military for conducting a "genocide" campaign in southern Guerrero state, where a rebel group was active.
It says hundreds of people were killed or disappeared, and thousands more were illegally detained or tortured in the so-called Dirty War.
The report is the work of a special prosecutor's office, named by President Vicente Fox four years ago to probe alleged rights abuses.
The New York Times quotes the prosecutor, Ignacio Carrillo Prieto as saying some changes will be made before the report is released officially.
Some information for this report was provided by AFP.