Russian groups and other foreign adversaries have unleashed an extensive disinformation campaign to undermine confidence in the election, and senior US officials are worried that Moscow’s efforts could continue to stoke political discord until the election is certified in January.

On Monday night, just hours before an election that polls show is the most closely fought in decades, intelligence, law enforcement and election defence agencies released a statement stressing once more — and in strong terms — their concern.

The Office of the Director of National Intelligence, the Cybersecurity and Infrastructure Security Agency and the FBI said in a joint statement that foreign adversaries led by Russia were “conducting additional influence operations intended to undermine public confidence in the integrity of US elections and stoke divisions among Americans”.

Two weeks ago, they warned of post-election violence. Over the last 10 days, they have now issued three warnings about Russian attempts to undermine faith in the election. And Jen Easterly, the director of the Cybersecurity and Infrastructure Security Agency, said her organisation would give regular updates.