WASHINGTON — Russian agents who favored Donald Trump's presidential candidacy harnessed the major players of America's tech industry in a sophisticated propaganda effort that was far more extensive than originally understood, according to a detailed analysis prepared for the Senate intelligence committee.

The Russian efforts included an attempt to suppress the votes of African-Americans.

Researchers combed through millions of posts from Facebook, Instagram, Twitter and YouTube created by the Internet Research Agency, the St. Petersburg-based firm run by a close ally of Russian President Vladimir Putin whose key executives have been indicted by special counsel Robert Mueller on charges of defrauding the United States.

Two separate reports on the operation were prepared for senators, both of which were obtained by NBC News. Both sets of researchers found, as Mueller did, that the Internet Research Agency set out in the 2016 presidential election to help Trump and hurt Hillary Clinton, the Democratic nominee, in part by inflaming right-wing conspiracy theories and seeking to engender distrust among — and suppress the vote of — left-leaning groups, including African-Americans.

The Russians set up 30 Facebook pages targeting black Americans, the researchers found, and 10 YouTube channels that posted 571 videos related to police violence against African-Americans. YouTube, which is part of Alphabet, the holding company for Google, was not correct when it said in a statement last year that Russian content did not target a segment of U.S. society, the researchers concluded.

Alex Stamos, the former head of security at Facebook and now an NBC News analyst, said, "[The African-American targeting] is a really important reminder that upsets the conventional wisdom from a lot of people that social media was mainly used to manipulate people on the right... but it was also on the left."

The Russians also set up hotlines that encourage people to discuss sexual or other personal problems the researchers found, raising the possibility they could use the information later to blackmail people. Through deceit, the Internet Research Agency recruited many Americans to take various political actions, the researchers found.

The post that drew the most attention featuring Trump emerged on Jan. 23, 2017, after his inauguration — a conspiracy theory asserting that President Barack Obama had refused to ban Sharia Law and encouraging President Trump to take action. It was shared 312,632 times from a page created by Russian propagandists.

The post with the most engagement that featured Donald Trump emerged after the election, on Jan. 23, 2017. It was a conspiracy theory about President Barack Obama refusing to ban Sharia Law. New Knowledge

The top post featuring Clinton came a month before the election, the researchers found — a soup of conspiracy theories alleging that she would win because of voter fraud and alluding to an armed uprising. It received 102,253 engagements, which can be anything from likes and shares to comments.

"This newly released data demonstrates how aggressively Russia sought to divide Americans by race, religion and ideology, and how the IRA actively worked to erode trust in our democratic institutions," said Senate Committee on Intelligence chairman Sen. Richard Burr, R-N.C.

Committee vice chair Sen. Mark Warner, D.-Va., said, "These attacks against our country were much more comprehensive, calculating and widespread than previously revealed. This should stand as a wakeup call to us all that none of us are immune from this threat, and it is time to get serious in addressing this challenge."

"It’s good for people to see this stuff," said Stamos. "It’s important for people to see when they interact with content online that this is what mass-produced influence or memes look like."

The Washington Post first reported Sunday on a draft of one of the reports, by Oxford University's Computational Propaganda Project and Graphika, a network analysis firm.

Click here to read the Oxford report.

The other group, led by New Knowledge, a cybersecurity firm that specializes in disinformation, counted 263,769,228 engagements with internet Research Agency content — including likes, comments and shares — on Facebook and Instagram. They said the total number of people who viewed the Russian-backed content is likely higher than the 126 million people Facebook said were exposed.

New Knowledge faulted U.S. social media companies for failing to come to grips with the extent to which their platforms are being used for foreign propaganda, and the researchers noted that Russian efforts to manipulate American voters continue mostly unabated.

Click here to read the New Knowledge report.

"The Instagram and Facebook engagement statistics belie the claim that this was a small operation — it was far more than only $100,000 of Facebook ads, as originally asserted by Facebook executives," the New Knowledge white paper said. "The ad engagements were a minor factor in a much broader, organically driven influence operation."

A Twitter spokesperson said, "Our singular focus is to improve the health of the public conversation on our platform, and protecting the integrity of elections is an important aspect of that mission. We've made significant strides since 2016 to counter manipulation of our service, including our release of additional data in October related to previously disclosed activities to enable further independent academic research and investigation."

In a statement, a Facebook spokesperson said, "Congress and the intelligence community are best placed to use the information we and others provide to determine the political motivations of actors like the Internet Research Agency. We continue to fully cooperate with officials investigating the IRA's activity on Facebook and Instagram around the 2016 election. We've provided thousands of ads and pieces of content to the Senate Select Committee on Intelligence ... [W]e've made progress in helping prevent interference on our platforms during elections, strengthened our policies against voter suppression ahead of the 2018 midterms, and funded independent research on the impact of social media on democracy."

A Google spokesperson said the company had conducted "an in-depth investigation across multiple product areas, and provided a detailed and thorough report to investigators."

"As we said at the time, videos on YouTube are viewable by anyone. Users can create videos intended for certain audiences, but there is no way to target by race on Google or YouTube."

The Russian social media effort, which unfolded alongside a separate Russian intelligence operation to hack and leak Democratic emails, was "intended to reinforce tribalism, to polarize and divide, and to normalize points of view strategically advantageous to the Russian government on everything from social issues to political candidates," the New Knowledge white paper said.

Some of the Facebook and Instagram ads linked to a Russian effort to disrupt the American political process and stir up tensions around divisive social issues werereleased by members of the U.S. House Intelligence committee on Nov. 1, 2017. Jon Elswick / AP file

"It was designed to exploit societal fractures, blur the lines between reality and fiction, erode our trust in media ... in government, in each other, and in democracy itself."

The U.S. government, the report noted, has done little to understand or deter the use of social media platforms by foreign propagandists.

Some of the key findings in the New Knowledge report:

YouTube was used more extensively than previously known. The Internet Research Agency (IRA) began making YouTube videos in September 2015, producing 1,107 videos across 17 channels. A few channels were active until July 2017.

The agency developed a collection of more than 3,840 persona accounts on Twitter; approximately 1.4 million people engaged with their tweets. They generated 72,801,807 engagements on their original content.

The posts display "a nuanced and deep knowledge of American culture, media, and influencers in each community the IRA targeted." Pepe the Frog memes were used to reach alt-right youth, but don't appear on pages aimed at older conservatives, "The IRA was fluent in American trolling culture."

The Internet Research Agency impersonated state and local news media on Twitter and Instagram, setting up approximately 109 Twitter accounts masquerading as news organizations, including 44 U.S.-focused Twitter handles that amassed 660,335 followers between them — with an average of 15,000 followers each. The accounts were bots posting like to articles, many of which were bogus.

The agency simultaneously worked hard to undermine trust in real news media both among left and right-right-leaning audiences.

There were dozens of posts extolling the virtues of Wikileaks and Julian Assange.

Thousands of conspiratorial tweets were advanced or amplified by fake right-wing personas, and included pseudoscience conspiracies about vaccines, paranormal activity and aliens, and anti-Semitic complaints about the "globalist" agenda.

The Russians sought to convey a narrative that the Mueller investigation was corrupt, and that the emerging Russia stories were a "weird conspiracy" pushed by "liberal crybabies."

Stamos said the Democratic Party will make an attractive target for disinformation peddlers as the 2020 presidential election approaches.

"It has lots of candidates, no clear front runner, lots of room to push candidates towards extremist positions... It's not only people on the alt-right and in the Trump universe being manipulated by Russians."