Any suggested involvement by him in collusion with Russia was a "detestable lie", Sessions declared - and had he been made aware of such collusion, he would have quit his key role in the campaign.

Sessions' appearance was about defending his reputation after sacked FBI director James Comey testified to the Senate Intelligence Committee last week - but the optics of his persistent rejection of questions on conversations with the President were yet another headache for the White House.

Independent senator Angus King accused the Attorney General of being selective in claiming he was upholding Justice Department policy on the President's private conversations with members of his cabinet.

"I am protecting the right of the President to assert [executive privilege] if he chooses, and there may be other privileges that apply," Sessions responded. "At this point I believe it's premature for me to deny the President a full and intelligent choice about executive privilege."

Democratic senator Ron Wyden went on the attack: "Americans don't want to hear that answers to relevant questions are privileged or off-limits," he said. "We are talking about an attack on our democratic institutions and stonewalling of any kind is unacceptable."

Sessions shot back: "I am not stonewalling - I am following the historic policies of the Department of Justice.

"I cannot and will not violate my duty to protect the confidential communications I have with the President."

The presidential conversations on which Sessions refused to shed light were any that might have transpired about the Russia investigation or Comey's sacking - and even if Trump had asked him to leave a meeting in the Oval Office, as alleged by Comey.

Despite recusing himself from any Justice Department consideration of "this Russia thing", as Trump calls it, Sessions argued that the reason for his recusal was a departmental ban on its staff having anything to do with investigations of political campaigns in which they had played a part.

"I have never met with or had any conversations with any Russians or any foreign officials concerning any type of interference with any campaign or election in the United States," he said.

"I recused myself from any investigation into the campaigns for president, but I did not recuse myself from defending my honour against scurrilous and false allegations," he insisted.

Questioned about a reported third meeting, when he and Russian ambassador Sergey Kislyak were present at Washington's Mayflower Hotel in April 2016, Sessions became sharp: "If any brief interaction occurred in passing with the Russian ambassador during that reception, I do not remember it ??? [and if we did speak, it was] certainly nothing improper."

He rejected Comey's claim that Sessions had merely shrugged when the former FBI boss had "implored" him to stop Trump from engineering one-on-one meetings such as that in which Comey says Trump asked him to back off investigating disgraced former national security adviser Michael Flynn.

"Following a routine morning threat briefing, Mr Comey spoke to me and my chief of staff. While he did not provide me with any of the content of the substance of the conversation, Mr Comey expressed concern about proper communications protocol. I responded ??? by agreeing that the FBI and the Department of Justice needed to be careful to follow department policies regarding appropriate contact with the White House."

Sessions did reveal that, even before their Senate confirmation, he and his deputy Rod Rosenstein had discussed Comey's handling of the investigation into Democrat candidate Hillary Clinton's email server - and on that, they had decided the FBI would need a "fresh start" and that Comey would be sacked.

Sessions insisted too that in participating in Comey's ouster, he had not breached his recusal, because he had had nothing to do with his department's Russia probe, whereas a decision on Comey's fate and the management of the FBI was an appropriate decision about the entire department and not about just one of its thousands of investigations.

The Clinton saga was the basis of their recommendation to Trump on sacking Comey, but within days of its release, Trump contradicted it, claiming that the reason was always "the Russia thing".

Sessions said that, by dint of his recusal, he would not be involved in any effort, should one eventuate, to sack Robert Mueller, the quasi-independent special counsel appointed by the Justice Department to investigate the Russian meddling and associated matters - such as Comey's demise.

"I wouldn't think that would be appropriate for me to do," he said.

The possibility that Trump might attempt to dismiss Mueller came into the political discourse late on Monday - when Trump friend and right-wing media operator Christopher Ruddy said in a TV interview that Trump was considering precisely that.

Ruddy made his sensational claim against a backdrop of repeated questioning of Mueller's appointment by high-profile conservatives on social media.

But in testimony to Congress earlier on Tuesday, Rosenstein said he could comply with such a presidential request only if the President's order was "lawful and appropriate".

As a result of Sessions' recusal, Rosenstein argued that he alone could sack Mueller, adding: "I'm not going to follow any orders unless I believe those are lawful and appropriate orders ??? As long as I'm in this position, he's not going to be fired without good cause."