The Kremlin on Tuesday rejected Washington's accusations that Russia tried to disrupt the 2016 presidential vote and sought to demoralise African-Americans, calling the charges incomprehensible.

According to a new report for the US Senate, the primary goal of Russia's Internet Research Agency (IRA) was to deepen divisions in US society and convince Democrat-favouring liberals - including Latinos, youths and the LGBTQ community - not to vote.

The most extensive analysis yet of thousands of IRA ads and posts across social media in 2015-2017 showed an emphasis on provoking the anger of black Americans so that they would stay home on election day.

For example, the IRA-created account "Blacktivist" sent out messages on the Democratic candidate such as: "No lives matter to Hillary Clinton. Only votes matter to Hillary Clinton."

Another IRA account, "Black Matters", posted on Facebook: "Cops kill black kids. Are you sure that your son won't be the next?"

Russian President Vladimir Putin's spokesman Dmitry Peskov said the report by the Computational Propaganda Project at Oxford University and social media specialists Graphika caused "nothing but incomprehension."

"It voices absolutely general charges and accusations and some of them are absolutely unclear to us," Peskov told reporters on a conference call.

"We are reproached that someone critically thinks of a situation in this or that social sphere in the United States but it is not explained what Russia has to do with it," he said.

He reiterated Russia's long-standing position that any such claims were unfounded.

"The Russian state, the Russian government had and has nothing to do with any interference, especially one that is described in such abstract terms," Peskov added.

The IRA is believed to have been set up by Yevgeny Prigozhin, a businessman close to Putin, as a propaganda tool.

Russia has been accused of manipulating the 2016 US presidential vote through a vast propaganda campaign in favour of Donald Trump.

US investigators are probing alleged collusion between Russian agents and Trump's campaign.