The Russian influence campaign on social media in the 2016 election made an extraordinary effort to target African-Americans, used an array of tactics to try to suppress turnout among Democratic voters, and unleashed a blizzard of activity on Instagram that rivalled or exceeded its posts on Facebook, according to a report produced for the U.S. Senate Intelligence Committee.

The report adds new details to the portrait that has emerged over the last two years of the energy and imagination of the Russian effort to sway U.S. opinion and divide the country, which the authors said continues to this day.

“Active and ongoing interference operations remain on several platforms,” says the report, produced by New Knowledge, a cybersecurity company based in Austin, Tex., along with researchers at Columbia University and Canfield Research LLC. One continuing Russian campaign, for instance, seeks to influence opinion on Syria by promoting Bashar al-Assad, the Syrian president and a Russian ally in the brutal conflict there.

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The New Knowledge report, which was obtained by the New York Times in advance of its scheduled release on Monday, is one of two commissioned by the Senate committee on a bipartisan basis. They are largely based on data about Russian operations provided to the Senate by Facebook, Twitter and other companies whose platforms were used.

The second report was written by the Computational Propaganda Project at Oxford University along with Graphika, a company that specializes in analyzing social media. The Washington Post first reported on the Oxford report on Sunday.

The Russian influence campaign in 2016 was run by a St. Petersburg company called the Internet Research Agency (IRA), owned by businessman Yevgeny V. Prigozhin, who is a close ally of President Vladimir Putin. Mr. Prigozhin and a dozen of the company’s employees were indicted in February as part of the investigation of Russian interference by Robert Mueller, the U.S. special counsel.

Both reports stress that the IRA created social-media accounts under fake names on virtually every available platform. A major goal was to support Donald Trump, first against his Republican rivals in the presidential race, then in the general election, then as President since his inauguration.

Creating accounts designed to pass as belonging to Americans, the IRA spread its messages not only via Facebook, Instagram and Twitter, which have drawn the most attention, but also on YouTube, Reddit, Tumblr, Pinterest, Vine and Google+, among other platforms. Its attack on the United States used almost exclusively high-tech tools created by U.S. companies.

The New Knowledge researchers discovered many examples of the Russian operators building an audience with one theme and then shifting to another, often more provocative set of messages. For instance, an Instagram account called @army_of_jesus_ first posted in January, 2015, images from The Muppet Show, then shifted to The Simpsons and by early 2016, became Jesus-focused. Multiple memes associated Jesus with Mr. Trump’s campaign and Satan with Hillary Clinton’s.

The Russian campaign was the subject of Senate hearings last year and has been widely scrutinized by academic experts. The new reports largely confirm earlier findings: that the campaign was designed to attack Ms. Clinton, boost Mr. Trump and exacerbate existing divisions in U.S. society.

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But the New Knowledge report gives particular attention to the Russians’ focus on African-Americans, which is evident to anyone who examines collections of their memes and messages.

“The most prolific IRA efforts on Facebook and Instagram specifically targeted black American communities and appear to have been focused on developing black audiences and recruiting black Americans as assets,” the report says. Using Gmail accounts with American-sounding names, the Russians recruited and sometimes paid unwitting U.S. activists of all races to stage rallies and spread content, but there was a disproportionate pursuit of African-Americans, it concludes.

The report says that while “other distinct ethnic and religious groups were the focus of one or two Facebook Pages or Instagram accounts, the black community was targeted extensively with dozens.” In some cases, Facebook ads targeted users who had shown interest in particular topics including black history, the Black Panther Party and Malcolm X. The most popular of the Russian Instagram accounts was @blackstagram, with 303,663 followers.

The IRA also created a dozen websites disguised as African-American in origin, with names such as blackmattersus.com, blacktivist.info, blacktolive.org and blacksoul.us. On YouTube, the largest share of Russian material covered the Black Lives Matter (BLM) movement and police brutality with channels called Don’t Shoot and BlackToLive.

The report does not seek to explain the heavy focus on African Americans. But the IRA’s tactics echo Soviet-propaganda efforts from decades ago that often highlighted racism and racial conflict in the United States, as well as recent Russian influence operations in other countries that sought to stir ethnic strife.

Renée DiResta, one of the report’s authors and director of research at New Knowledge, said the IRA “leveraged preexisting, legitimate grievances wherever they could.” As the election effort geared up, the BLM movement was at the centre of national attention in the United States, so the Russian operation took advantage of it, she said – and added “Blue Lives Matter” material when a pro-police pushback emerged.

“Very real racial tensions and feelings of alienation exist in America and have for decades,” Ms. DiResta said. “The IRA didn’t create them. It exploits them.”

Of 81 Facebook pages created by the IRA in the Senate’s data, 30 targeted African-American audiences, amassing 1.2 million followers, the report finds. By comparison, 25 pages targeted the political right and drew 1.4 million followers. Just seven pages focused on the political left, drawing 689,045 followers.

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While the right-wing pages promoted Mr. Trump’s candidacy, the left-wing pages scorned Ms. Clinton while promoting Senator Bernie Sanders and Jill Stein, the Green Party candidate. The voter-suppression effort was focused particularly on Mr. Sanders’s supporters and African-Americans, urging them to shun Ms. Clinton in the general election and either vote for Ms. Stein or stay home.

Whether such efforts had a significant effect is difficult to judge. Black voter turnout declined in 2016 for the first time in 20 years in a presidential election, but it is impossible to determine whether that was the result of the Russian campaign.

The New Knowledge report argues that the IRA’s presence on Instagram has been underestimated, and may have been as effective or more effective than its Facebook effort. The report says there were 187 million engagements on Instagram – users “liking” or sharing the content created in Russia – compared to 76.5 million engagements on Facebook.

In 2017, as the U.S. news media focused on the Russian operations on Facebook and Twitter, the Russian effort shifted strongly to Instagram, the report says.

The New Knowledge report criticizes social-media companies for misleading the public.

“Regrettably, it appears that the platforms may have misrepresented or evaded in some of their statements to Congress,” the report says, noting what it calls one false claim that specific population groups were not targeted by the influence operation and another that the campaign did not seek to discourage voting.

“It is unclear whether these answers were the result of faulty or lacking analysis, or a more deliberate evasion,” the report says.

The report suggests a grudging respect for the scale and creativity of Russian influence operations. But the Russians were not eager to take credit for their own efforts.

After the election, the report says, the IRA put up some 70 posts on Facebook and Instagram that mocked claims that Russia had interfered in the election.

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“You’ve lost and don’t know what to do?” one such post said. “Just blame it on Russian hackers.”