Newly declassified files from the U.S. Embassy in Jakarta confirm the extent to which American officials supported the killings of hundreds of thousands of Indonesians in the 1960s, as the U.S. worked to keep Southeast Asia from falling into Communist control.

The U.S. supported a narrative pushed by the Indonesian military that blamed Communists for a failed coup in 1965, targeting the anti-American President Sukarno.

This narrative emboldened the Indonesian military, paramilitaries and others to oversee the killings of 500,000 Indonesians who were suspected Communists, including students and union members.

"These newly released documents make clear that U.S. officials had detailed knowledge of the mass killings in Indonesia in 1965-66."—Phelim Kine, Human Rights Watch

"The U.S. was following what was happening very closely, and if it weren't for its support, you could argue that the army would never have felt the confidence to take power," said John Roosa, author of the book Pretext for Mass Murder, about the events, in an interview with the New York Times.

In a secret cable sent from the Embassy to Washington, D.C. in November 1965, an official detailed the efforts of provinces to repress suspected members of the Indonesian Communist Party (PKI) and its executions of prisoners as a means of controlling prison populations.

"Both in the provinces and Djakarta, repression of the PKI continued, with the main problem that of what to feed and where to house the prisoners," wrote a political affairs counselor. "Many provinces appear to be successfully meeting this problem by executing their PKI prisoners, or by killing them before they are captured."

According to some of the 39 cables released by the National Security Archive on Tuesday, Washington also withheld aid from Indonesia until Sukarno was removed from power, and called the rise of his successor, the military dictator Suharto who had ordered many of the mass killings, "a fantastic switch."

Following the release of the documents, Human Rights Watch called for a full accounting of U.S. involvement in the killings. "These newly released documents make clear that U.S. officials had detailed knowledge of the mass killings in Indonesia in 1965-66," said Phelim Kine, the group's deputy Asia director. "The U.S. government now needs to release the remaining documents, not only for the historical record of one of the 20th century's worst atrocities, but as a long overdue step toward bringing redress to the victims."

A headline on the story in the New York Times on Wednesday suggested that the U.S. merely "stood by" while the killings took place without intervening—a characterization that was criticized by Adam Johnson of FAIR as glossing over the extent to which the U.S. was involved.