The Guatemalan authorities have detained 14 former military officials on charges of human rights abuses during the country's 36-year armed conflict.
Among those detained was Manuel Benedicto Lucas Garcia, 83, a former general and brother of former president Fernando Romeo Lucas Garcia.
A former minister of the interior was also arrested.
Many of the detainees allegedly worked where a mass grave was found.
Manuel Benedicto Lucas Garcia is a former army commander said to have been involved in founding Guatemala's paramilitary groups.
His brother ruled Guatemala from July 1978 to March 1982.
Both face charges of crimes against humanity and being involved in the disappearances of hundreds of people.
The Guatemalan attorney general, Thelma Aldana, said they were being detained in connection with the disappearance of at least 558 indigenous people between 1981 and 1988 in a military zone in Coban, in the northern department of Alta Verapaz.
She said this was "one of the largest cases of forced disappearances in Latin America".
Military Zone 21 currently houses a military training centre, but in 2012 four mass graves were found containing the bodies of "non-combatant civilians identified by survivors" said Mrs Aldana.
In 2012 a group of five ex-paramilitaries who had operated in Zone 21 were given life sentences of 7,710 years for their involvement in the mass killings.
According to prosecutors, survivors said the army had killed, in one massacre alone, 256 indigenous people - mostly women, children and old people from the Mayan Achi ethnic group.
The army had accused the local poor Mayan farmers community of supporting left-wing guerrillas operating in the area.
Prosecutors said testimonies from survivors had helped officials locate the mass graves in Zone 21 Coban and connect them to the officers.
Mario Polanco, the director of an organisation representing the families of the victims of the conflict, the Mutual Support Group (GAM), described as "historic" the arrest of the 14 ex-military officers.
"These are people who had thought they were masters of the universe and Guatemala," he said.
Guatemala's armed conflict ended in 1996 after a peace accord. In the last 10 years the country has begun prosecuting human rights cases from its past but few high-level officials have been jailed.
The conflict pitted right-wing governments against left-wing insurgents and led to nearly 250,000 deaths.
A UN-backed truth commission said the armed forces carried out more than 80% of human rights abuses during the conflict.