Guatemala's internal armed conflict took place between 1960 and 1996.
More than 200,000 men, women and children were murdered or disappeared.
General Efraín Ríos Montt was in office between March 1982 and August 1983.
The conflict ended in 1996 with the signing of a Peace Accord.
A UN-sponsored Commission of Historical Clarification said the Guatemalan state was responsible for most abuses.
Reports that Guatemala may open the door to an amnesty for former President Effrain Ríos Montt would be a travesty of justice and send the country back more than a decade, said Amnesty International.
Ríos Montt is facing a re-trial for genocide and crimes against humanity.
“This is an alarming new development that, if confirmed, would set the country back decades. Amnesties can never be applied to genocide and crimes against humanity,” said Sebastian Elgueta, Guatemala researcher at Amnesty International.
“With such a decision, Guatemala’s authorities would destroy, with one signature, decades of progress when it comes to justice for the tens of thousands of people who died and were disappeared during the dark years of the conflict.”
According to media reports, Guatemala’s Constitutional Court has ordered that more details be provided as to why Ríos Montt’s request for amnesty was refused. This raises the possibility that amnesty is being seriously considered, closing the case against him and others facing similar charges.
“Awarding Rios Montt an amnesty would mean he could get away with genocide. This decision would also benefit others who are accused or convicted of enforced disappearances, systematic sexual violence, torture and killings. It would be a monumental disaster for the victims and their relatives and it must never happen,” said Sebastian Elgueta.
“Amnesties are a tragedy for victims as they block truth, justice and reparation; and for society as a whole, as they prevent a full examination and acknowledgement of what occurs during periods of widespread human rights abuses.”
In May 2013 Ríos Montt was tried, convicted and sentenced to 80 years for his role in the killing of nearly 2,000 Ixil Indigenous Peoples between 1982 and 1983. The conviction was overturned 10 days later by the Constitutional Court on a technicality.
Between 1960 and 1996, Guatemala was immersed in a bloody internal armed conflict that pitted the army against guerrilla groups. Across the country, more than 200,000 men, women and children were murdered or disappeared during this 36-year-long war, most of whom were Indigenous.