Donald Trump has dismissed a US intelligence assessment that Russia is meddling in the 2020 election to help his re-election as a Democrat "hoax", amid a row over a briefing with Congress last week.

"Another misinformation campaign is being launched by Democrats in Congress saying that Russia prefers me to any of the Do Nothing Democrat candidates who still have been unable to, after two weeks, count their votes in Iowa," the president tweeted, adding "Hoax number 7!"

It comes after America's top election security official, Shelby Pierson, warned the House Intelligence Committee that the Kremlin was interfering in the 2020 presidential campaign to aid Mr Trump's re-election in a classified briefing on February 13.

More than two dozen Democrats and Republicans sit on the committee, and the details of the briefing are thought to have been related to Mr Trump.

The US president was furious with his acting director of national intelligence (DNI), Joseph Maguire, and his aides for speaking to Congress and accused them of being "disloyal", according to the Washington Post.