Russians charged with interfering in 2016 US election
His office said 13 Russians and three Russian entities had been indicted by a federal grand jury in Washington DC.
The companies include the so-called "troll farm" the Internet Research Agency, based in Saint Petersburg. It is accused of having "a strategic goal to sow discord in the US political system, including the 2016 US presidential election".
The 37-page indictment sheet alleges that the Russians' operations "included supporting the presidential campaign of then-candidate Donald J Trump... and disparaging (Democratic opponent Hillary Clinton".
Some of the defendants are said to have used computer systems and stolen real identities to hide their Russian origins.
"Defendants, posing as US persons and creating false US personas, operated social media pages and groups designed to attract US audiences," reads the charge sheet.
It adds that they and co-conspirators created and controlled many Twitter accounts designed to appear as if they were controlled by Americans.
False identities were also used to buy advertisements and stage political rallies, the indictment says.
Those involved are said to have begun discussing their plans as early as 2014.
All the defendants are charged with conspiracy to defraud the United States. Three are also accused of other conspiracy to commit wire fraud and bank fraud. Five are charged with aggravated identity theft.
Donald Trump's campaign and transition teams have been accused of colluding with Russian agents to influence the election. The president - who has previously denounced Mueller's investigation as a "witch hunt" - and the Kremlin deny wrongdoing.
Mueller is conducting a criminal inquiry into the affair. One aide has pleaded guilty to lying to the FBI while two others have been charged with federal crimes.
The indictment broadly echoes the conclusions of US intelligence agencies. In January 2017 an intelligence community assessment found that Russian had meddled in the US election, and that its goals eventually included aiding Trump in his bid to enter the White House.
Donald Trump: 'no collusion!'
White House spokeswoman Sarah Sanders said Donald Trump had been briefed on the indictment announced on Friday.
A while later the president tweeted to insist that "the Trump campaign did nothing wrong - no collusion!". He did acknowledge, however, a Russian "anti-US campaign" which he said had begun in 2014, "long before" he announced his intention to run for the White House.
"This indictment serves as a reminder that people are not always who they appear to be on the internet," Deputy Attorney General Rod Rosenstein said at a news briefing on Friday. "The indictment alleges that the Russian conspirators want to promote discord in the United States and undermine public confidence in democracy. We must not allow them to succeed."
He also said there was no allegation in the charges that the defendants' behaviour had altered the outcome of the election.
"We have known that Russians meddled in the election, but these indictments detail the extent of the subterfuge. These Russians engaged in a sinister and systematic attack on our political system. It was a conspiracy to subvert the process, and take aim at democracy itself," said House of Representatives Speaker Paul Ryan in a statement.
"For all those who have been asking 'where is the evidence of a crime?' - this is it. This is the criminal conspiracy. This is what President Trump and his allies have repeatedly called a 'hoax' and 'fake news'. Today's indictment shows precisely how the Russians worked to help the Trump campaign, in startling and extensive detail," said Democratic Representative Elijah Cummings.
The evidence contained in indictment has been dismissed by the Kremlin. "Thirteen people interfered in the US elections?! Thirteen against an intelligence services budget of billions? Against intelligence and counterintelligence, against the latest developments and technologies? Absurd? "Yes," Russian Foreign Ministry spokeswoman said Maria Zakharova in a Facebook post.
Facebook and Twitter have both declined to comment on the indictment.
This is a developing story which we are updating as the information becomes available.