WASHINGTON (AFP) - US President Donald Trump's administration on Monday (March 20) insisted "nothing has changed" after revelations that the FBI is investigating his campaign's links to Russia and said there was no collusion.

"There is NO EVIDENCE of Trump-Russia collusion and there is NO EVIDENCE of a Trump-Russia scandal," a senior administration official said in a written statement after FBI director James Comey's explosive Congressional testimony.

Trump followed up with a series of tweets, providing his take on lengthy testimony, claiming - misleadingly - that the FBI and NSA testified that "Russia did not influence electoral process."

In testimony, FBI Director James Comey and NSA director admiral Mike Rogers stated that Russia did not hack ballot counts, but did try to sway the election in Trump's favour.

Trump also focused on leaks of information about his aides' ties to Russia and appeared to imply that his predecessor Barack Obama was among those who could have provided the information to journalists.

"FBI Director Comey refuses to deny he briefed President Obama on calls made by Michael Flynn to Russia," Trump tweeted.