The US Justice Department on Monday abruptly dropped its criminal case against a company controlled by an ally of Russian President Vladimir Putin, which allegedly funded the campaign to meddle in the United States' 2016 elections.

Just weeks before the trial was to begin, the Justice Department announced it was withdrawing the eight-count indictment of Concord Management and Consulting, a company owned by Yevgeny Prigozhin.

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Concord, which funds the St Petersburg-based troll factory the Internet Research Agency, was part of an indictment against 13 Russian individuals and three companies - one of the major outcomes of Special Counsel Robert Mueller's 22-month investigation into Russian interference in the 2016 vote.

The Internet Research Agency, Mueller charged, actively pumped disinformation, memes and fake news into social media through false accounts to influence US voters and tilt the election four years ago to help President Donald Trump.

Like Mueller, US intelligence chiefs concluded that the Concord-run operation was one half of a sweeping campaign overseen by Putin - the other half was hacking by Russian intelligence - to help Trump and hurt his rival, Democrat Hillary Clinton.

In a filing in Washington federal district court, the Justice Department said that Concord's tactics of trying to use US law and court procedures to prise out classified intelligence related to the evidence against it was a threat to national security.

"The government has concluded that further proceedings as to Concord, a Russian company with no presence in the United States and no exposure to meaningful punishment in the event of conviction, promotes neither the interests of justice nor the nation's security," it said.

Laywers representing Concord Management and Consulting LLC, walk out of federal court in Washington, after pleading not guilty on behalf of the company in May 2018. [File: Andrew Harnik/AP]

Concord was the only one of three Russian companies and 25 Russian individuals charged by Mueller to be brought to trial.

The rest are considered out of reach of US law, but the charges against them - including Prigozhin - remain in place.

The Justice Department said recent rules changes regarding evidence based on classified US intelligence made it harder to proceed in the case without exposing secrets.