President Ernesto Geisel ruled Brazil from 1974 to 1979, toward the end of the country's two decade long military dictatorship.

According to the CIA document - dug up by Matias Spektor, head of the international relations department at the Getulio Vargas Foundation think tank - Geisel gave clear instructions to the head of the national intelligence agency that such killings should continue.

"On 1 April, President Geisel told General Figueiredo that the policy should continue, but that great care should be taken to make certain that only dangerous subversives were executed," reads the document.

The CIA report noted that Geisel and the intelligence head, Joao Baptista Figueiredo, decided that whenever a potential target was apprehended by the army, Figueiredo would have to give approval "before the person is executed."

The CIA report was issued on April 11, 1974 by then director William Colby and sent to the secretary of state, Henry Kissinger.

Memory of the 1964-1985 military dictatorship has faded for most Brazilians but not disappeared. Since then, the country has suffered repeated bouts of instability, economic crisis and corruption scandals, prompting some like presidential candidate Jair Bolsonaro to view the brutal period with open nostalgia.

Spektor wrote on Facebook that the document was "the most disturbing I've read in 20 years of researching."

A National Truth Commission, which revealed the extent of torture and repression, listed 434 people executed or who disappeared during the dictatorship. But a 1979 amnesty meant that no one was ever prosecuted for crimes committed under the regime.

Vera Rotta, who worked at the human rights secretariat under the leftist governments of Luiz Inacio Lula da Silva, said the document is a smoking gun.

"We never had in our hands a document where it literally said: 'We will execute people.' (The military) always argued that executions were just isolated cases."

The declassified CIA document can be seen at:

https://history.state.gov/historicaldocuments/frus1969-76ve11p2/d99?platform=hootsuite.