(Reuters) - The Senate committee investigating Russian interference in the 2016 U.S. election said on Tuesday that the Kremlin’s best-known propaganda arm increased its social media activity after that vote, adding to concerns about foreign meddling in the current 2020 campaign.

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The Senate Intelligence Committee, which has managed to operate under bipartisan consensus when other congressional panels have not, said in a report that activity by the St. Petersburg-based Internet Research Agency “increased, rather than decreased, after Election Day 2016.”

IRA-linked account activity jumped more than 200% on Instagram and more than 50% on Facebook, Twitter and YouTube, the committee said. The IRA and related entities and people were indicted by special counsel Robert Mueller.

The committee, led by Republican Chairman Richard Burr and Democratic Vice Chairman Mark Warner, also concluded that African-Americans had been the group most targeted by Russian influence campaigns that sought to exacerbate tensions and increase the election prospects of President Donald Trump.

“By flooding social media with false reports, conspiracy theories, and trolls, and by exploiting existing divisions, Russia is trying to breed distrust of our democratic institutions and our fellow Americans,” Burr said. He called for Congress, the executive branch and the social media companies to redouble their efforts at transparency and education.

The report by the Republican-controlled committee reaffirmed findings by the U.S. intelligence community and Mueller that the Kremlin pursued an influence operation through social media and other means aimed at throwing the 2016 U.S. presidential election to Trump over his Democratic opponent, Hillary Clinton.

In doing so, the Senate report contradicted allegations by Trump’s personal attorney Rudolph Giuliani and others that Ukraine colluded with Democrats to undermine Trump’s campaign, as well as charges by the White House and Trump allies - including Representative Devin Nunes - that Russia actually aided Clinton’s candidacy.

“The Committee found that IRA social media activity was overtly and almost invariably supportive of then-candidate Trump, and to the detriment of Secretary Clinton’s campaign,” said the report, the latest in a series from the senators related to 2016 interference.

On YouTube, all of the IRA’s political videos were thematically opposed to Clinton. Some aimed at dissuading black Americans to vote, while others suggested they vote for Green Party candidate Jill Stein.

The report detailed an extraordinarily sophisticated operation that witnesses described as the most successful influence campaign in history, one that will be studied globally for decades. The effort went well beyond hacking, Facebook and Twitter and swept up Medium, Tumblr and Pinterest.

One Facebook page with more than 200,000 followers, “Army of Jesus,” posted only pro-Christian messages until just before the election. Then it blared a false story asserting that Clinton had approved removing the word God from the U.S. Pledge of Allegiance.

False and slanted stories often spread more rapidly than professional, independent news. In the key swing state of Michigan, one study found that the ratio “was most disproportionate the day before the election.”

The panel recommended that Congress consider new laws requiring disclosure of who pays for election-related online advertising. Members expressed special alarm at sophisticated micro-targeting, noting that the IRA could have been much more effective in swing states if it had used Facebook tools for customizing audiences instead of just using geography.

“Propagandists will be able to continue to utilize increasingly advanced off-the-shelf capabilities to target specific individuals with highly targeted messaging campaigns,” it wrote in the detailed, 85-page report.

It also said social media companies, which have come under fire for allowing propaganda to flourish, should share more information about what they find on their platforms.

In the long term, the committee said, resistance to foreign manipulation will require building media literacy from an early age, perhaps with federal funding but led by state and local educational institutions.