US President Donald Trump denied Sunday having asked then FBI director James Comey to drop an investigation into former national security advisor Michael Flynn, who has since pleaded guilty to lying to the FBI about discussions with Russia.

"I never asked Comey to stop investigating Flynn. Just more Fake News covering another Comey lie!", Trump said in a tweet.

On Saturday, Trump again insisted he and his campaign had not colluded with Moscow in last year's election, and shifted blame on the Justice Department and his rival Hillary Clinton