Former National Security Adviser John Bolton has made a dramatic return to Twitter following his unexplained hiatus since his resignation in September, saying the White House blocked access to his personal account and suggested they are fearful of what he might say.

His name has repeatedly surfaced in the impeachment hearings as a witness to key events, and on Friday afternoon he tweeted: "To those who speculated I went into hiding, I’m sorry to disappoint!"

The first of three tweets appeared on Friday morning, amid a wide-ranging interview Donald Trump gave on Fox & Friends.

Mr Bolton wrote: "The first of Glad to be back on Twitter after more than two months. For the backstory, stay tuned........"

Mr Trump was asked whether he was involved in blocking Mr Bolton’s Twitter account. He replied: "No, of course not, I had a good relationship with John.”

But Mr Bolton appeared to hit back later in the day, writing: "We have now liberated the Twitter account, previously suppressed unfairly in the aftermath of my resignation as National Security Advisor. More to come....."

This was followed by an afternoon update saying: "Re: speaking up -- since resigning as National Security Advisor, the @WhiteHouse refused to return access to my personal Twitter account. Out of fear of what I may say? To those who speculated I went into hiding, I’m sorry to disappoint!"

Donald Trump attacks 'tough guy' John Bolton, accusing him of pushing for US invasion of Iraq

The tweets arrived following an historic week of hearings on Capitol Hill, where high-level current and former officials appeared before the House Intelligence Committee as part of the public impeachment inquiry against Mr Trump.

Mr Bolton was invited - but not subpoenaed - to appear, but did not do so.

Former National Security Council official Dr Fiona Hill was among those who testified on Mr Bolton's role in Mr Trump’s call with Ukrainian president Volodymyr Zelensky in July.

She said Mr Bolton said that Mr Trump's personal attorney Rudy Giuliani was a “hand grenade” and wanted to distance himself from “whatever drug deal" US ambassador to the EU Gordon Sondland and acting chief of staff Mick Mulvaney were "cooking up".