13 Russians indicted for election interference

According to the unsealed indictment the accused conspired -- from 2014 until today -- to interfere "with the US political and electoral processes, including the presidential election of 2016."

Mueller alleges that the group posed as Americans and controlled social media accounts that focused on divisive social and political issues.

Under the management of Yevgeny Prigozhin, a close ally of Vladimir Putin, the group reached "significant numbers" of Americans, according to the indictment.

They had a "strategic goal to sow discord in the US political system" and by mid-2016 were supporting Donald Trump's campaign and disparaging Hillary Clinton.

The group was based in Putin's home town of Saint Petersburg, but some of the accused traveled to the United States.

Stops included Nevada, California, New Mexico, Colorado, Illinois, Michigan, Louisiana, Texas, Georgia and New York.

An unnamed Texas-based American political operative is said to have instructed them to focus on so-called "purple states" which swing between Republican and Democratic control.

"Hundreds" of people were said to have been involved in the operation, working in shifts and with a budget of millions of dollars.

They allegedly targeted social media sites like Facebook, Twitter, YouTube and Instagram.

Two of the firms are said to have Russian government contracts.