US President Donald Trump has attacked former FBI Director James Comey as a "weak and untruthful slime ball", reacting to news accounts that cite Comey as searingly critical of the president in a memoir due to be published next week.
"It was my great honour to fire James Comey!" Trump said on Friday in a series of angry Twitter messages, adding he had been a terrible FBI director.
Trump fired Comey last May and has publicly criticised him since then but not to this extent.
Comey had been investigating allegations that Russia meddled in the 2016 presidential election and possible collusion between Russians and the Trump campaign. His firing led to the Justice Department appointing Special Counsel Robert Mueller to take over the Russia investigation.
Trump has denied any collusion, but the Russia probe has been an open sore for his presidency.
"James Comey is a proven LEAKER & LIAR," Trump said. He also accused Comey of lying to congress, apparently referring to Comey's Senate testimony last June, when he said he needed to get his account of his conversations with Trump in the public sphere in the hope it might prompt the appointment of a special counsel.
Comey told lawmakers he had given copies of his memo memorialising his talks with Trump to people outside the Justice Department and asked a friend to share its contents with a journalist.
The former FBI director is doing a series of media interviews before the release of his book, A Higher Loyalty: Truth, Lies and Leadership, which news organisations have said paints a deeply unflattering picture of the president.
The interviews are Comey's first public comments since he testified before the Senate Intelligence Committee last June, when he accused Trump of firing him to undermine the FBI's Russia investigation.
In an interview broadcast on Friday on ABC's Good Morning America, Comey discussed his initial encounters last year with the new president. He described Trump as volatile, defensive and concerned more about how his own image than about alleged Russian meddling in the presidential election.
Comey said he cautioned Trump against ordering an investigation into a salacious intelligence dossier alleging an 2013 encounter with prostitutes in Moscow.
In the book, Comey wrote that Trump raised the intelligence dossier with him at least four times during meetings after Trump took office in January, according to the Washington Post, which obtained a copy.
The dossier was compiled by former British intelligence officer Christopher Steele about Trump's ties to Russia and included an allegation that involved prostitutes.
Trump denied the allegations and said he might want the FBI to investigate allegations in the dossier to prove they were not true, Comey told ABC.
"I said to him, 'Sir that's up to you but you want to be careful about that because it might create a narrative that we're investigating you personally and, second, it's very difficult to prove something didn't happen," Comey said.
Asked how bizarre that meeting with Trump was, Comey said: "Very weird. Really weird. It was almost an out of body experience for me. I was floating above myself looking down saying 'you're sitting here briefing the incoming president of the United States about prostitutes in Moscow.'"
In January 2017, US intelligence chiefs briefed Trump and his advisers on Russia's election meddling.
What struck him most, Comey told ABC, was that the conversation moved straight into a public relations mode, what they could say and how they would position Trump.