Donald Trump, the US president, has called for former FBI director James Comey to be jailed, accusing him of revealing classified information and of lying to Congress.
In addition to suggesting the former intelligence chief be incarcerated, Mr Trump called him "slippery" and a "slimeball" and said he would go down as the worst FBI director in history, during a Twitter rant which spanned the course of two hours on Sunday morning.
He also challenged accusations made by the former FBI director in a tell-all book that is due for release this week.
Mr Trump wrote: "The big questions in Comey's badly reviewed book aren't answered like, how come he gave up Classified Information (jail), why did he lie to Congress (jail), why did the DNC refuse to give Server to the FBI (why didn't they TAKE it), why the phony memos, McCabe's $700,000 & more?"
He added: "I never asked Comey for Personal Loyalty. I hardly even knew this guy. Just another of his many lies. His "memos" are self serving and FAKE!"
And shortly after came: "Slippery James Comey, a man who always ends up badly and out of whack (he is not smart!), will go down as the WORST FBI Director in history, by far!"
The two men have been involved in a ferocious war of words since the president fired Mr Comey last May amid the investigation into his 2016 campaign and Russian meddling in the election.
It was Mr Comey's firing that prompted the appointment of special counsel Robert Mueller.
Mr Comey later testified before the Senate Intelligence Committee that President Trump had asked him for "loyalty" at a January dinner. And that alone in the Oval Office, Mr Trump had said to him that he "hoped" he could let the investigation into former national security director Michael Flynn "go".
His evidence opened up the president to accusations of obstruction of justice, which Mr Trump has repeatedly and strongly denied.
Mr Comey's memoir, "A Higher Loyalty: Truth, Lies and Leadership" is released on Tuesday, but has already become a bestseller thanks to huge pre-publication sales.
On Sunday, ABC was due to air a lengthy interview to kick off Mr Comey's book tour, which was expected to attract millions of viewers.
Extracts that emerged last week showed Mr Comey likened the president to an "unethical" mob boss who is "untethered" to the truth, casts his inner circle poorly and details an obsession with a dossier written by former British spy Christopher Steele who wrote of rumoured engagements with prostitutes.
Mr Comey writes: "What is happening now is not normal. It is not fake news. It is not okay," describing "the forest fire that is the Trump presidency".
Meanwhile, Mr Trump's approval rating stands at its highest since his first 100 days in office at 40 per cent. The Washington Post-ABC News poll showed his popularity up four per cent from January.
Among white voters, he has 53 per cent support, up seven points since the beginning of the year and among white men without college degrees he is up six percent to 70 per cent.
Almost three-quarters of conservatives approve of the president in the latest poll, 74 per cent, up nine points from January.