Former secretary of state Henry Kissinger jeopardized US efforts to stop mass killings by Argentina’s 1976-83 military dictatorship by congratulating the country’s military leaders for “wiping out” terrorism, according to a large trove of newly declassified state department files.

The documents, which were released on Monday night, show how Kissinger’s close relationship to Argentina’s military rulers hindered Jimmy Carter’s carrot-and-stick attempts to influence the regime during his 1977-81 presidency.

Carter officials were infuriated by Kissinger’s attendance at the 1978 World Cup in Argentina as the personal guest of dictator Jorge Videla, the general who oversaw the forced disappearance of up to 30,000 opponents of the military regime.

At the time, Kissinger was no longer in office, having been replaced by Zbigniew Brzezinski after Carter defeated Gerald Ford in the 1977 presidential election, but the documents reveal that US diplomats feared his praise for Argentina’s crackdown would encourage further bloodshed.