WASHINGTON — With the blessing of a CIA bent on thwarting Soviet expansion, South American military juntas together formed a special unit charged with going to France and elsewhere abroad to exterminate leftist opposition leaders.

While the cooperation of military dictatorships was widely known, details about this special unit, called Teseo, were not, until the release Friday of the final 7,500 declassified U.S. documents shared with Argentina and the world.

President Donald Trump had promised his Argentine counterpart, Mauricio Macri, that the third and final tranche of U.S. documents would be shared, ending a process that began under President Barack Obama to make publicly available documents about a dark period in U.S. history. In all, roughly 47,000 U.S. military, diplomatic and intelligence cables pertaining to Argentina’s military junta were declassified.

“The release of records constitutes the largest declassification of the United States Government records directly to a foreign government in history,” said a letter from Trump to Macri accompanying the release. “My hope is that access to these records provides the people of Argentina information to help in the healing process.”

Details about the Teseo assassination unit were in a CIA document dated May 1976, part of a batch of documents delivered Friday that had to do with Operation Condor. That was a clandestine effort pushed hardest by Chilean dictator Augusto Pinochet that grew to involve military rulers in Argentina, Uruguay, Brazil, Paraguay and Bolivia.