US President Donald Trump says he is willing to be interviewed under oath by Special Counsel Robert Mueller, who is investigating Russian meddling in the 2016 US election.

"I'm looking forward to it, actually," Trump, speaking to reporters at the White House today, said of an interview with Mueller.

"I would do it under oath."

Although Trump has pledged cooperation with Mueller's probe before, Trump made his assertion as the White House and allies in Congress have stepped up attacks on the investigation's credibility and Trump himself has hedged on whether he would answer questions.

More recently, Trump's lawyers have been talking to Mueller's team about an interview, according to sources with knowledge of the investigation.

"I would like to do it as soon as possible," Trump said.

Trump, however, said that setting a certain date for an interview would be "subject to my lawyers and all of that".

Asked whether he thought Mueller would treat him fairly, Trump replied, "We're going to find out".

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Sources told Reuters earlier today that senior US intelligence officers including CIA Director Mike Pompeo have been questioned by the Special Counsel's team about whether Trump tried to obstruct justice in the Russia probe.

Such questioning is further indication that Mueller's criminal investigation into purported Russian interference in the US election and potential collusion by Trump's campaign includes examining the President's actions around the probe.

Trump repeated past statements that there was no collusion between the campaign and Russia and "there's no obstruction whatsoever".

US intelligence agencies have concluded that Russia interfered in the election campaign using hacking and propaganda to try to tilt the race in Trump's favour. Russia has denied it.

- Reuters, AAP