The influence campaigns of Russian-linked Twitter accounts in South America “are proxy elements to conquer the influence of the United States or the liberal democracies,” said another expert, Javier Lesaca Esquiroz, a visiting scholar at the School of International and Public Affairs at Columbia University.

“At some point, we can say this is the continuation of the Cold War that never ended,” Mr. Esquiroz said.

The analyses provided by the State Department did not prove that the Twitter accounts that stoked the South American protests were direct conduits of the Russian government. Instead, they were described as “likely linked to the Russian state” through computer-generated or other data mining analyses that support other government conclusions that tie them to Moscow.

A spokesman for the Russian Embassy in Washington, Nikolay Lakhonin, declined to comment on Thursday, asking only for “real evidence” of a Russian-linked disinformation campaign in South America. On Monday, after this article was published, Mr. Lakhonin pointed to Russian officials’ past responses to questions about interference in protests, including from Foreign Minister Sergei V. Lavrov, who told reporters in November that “we got used to the allegation that we are involved in everything that is going on on earth.”

“Recently we’ve been mentioned as the ones who meddle in the situation in Chile,” Mr. Lavrov said then, with a touch of exasperation. “And I was wondering why we are not mentioned in relation to the developments in Iraq, Lebanon and now in Bolivia.”