US President Donald Trump on Tuesday called for all cases stemming from Special Counsel Robert Mueller's investigation into Russian interference in the 2016 election to be "thrown out" and suggested he could bring a lawsuit over the matter.

Trump made the comments hours before a telephone conference call between lawyers for the president's former adviser, Roger Stone, and prosecutors. Stone was convicted on seven counts of lying to the US Congress, obstruction and witness tampering.

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Prosecutors initially called for Stone to receive a prison sentence of seven to nine years in the case but, after Trump publicly called the recommendation "unfair", the Justice Department scaled it back. That sent shock waves through Washington and prompted all four prosecutors to quit the case and one to quit the agency. The Justice Department said that it did not consult Trump before making its decision.

"Everything having to do with this fraudulent investigation is ... badly tainted and, in my opinion, should be thrown out," Trump said in a series of tweets.

"If I wasn't President, I'd be suing everyone all over the place ... BUT MAYBE I STILL WILL," Trump continued.

Asked about Trump's tweets on Tuesday in an interview with Fox News Channel, White House spokeswoman Stephanie Grisham alleged corruption and raised questions about the jury, adding: "He's frustrated, obviously, and who knows what he'll end up doing."

Stone was one of several former Trump associates to have been charged in the Mueller probe and one of only two to go to trial instead of pleading guilty.

Trump's tweets on Tuesday morning came days after the nation's top law enforcement official, Attorney General William Barr, said Trump's tweets made it "impossible" to do his job.

In a letter on Monday, more than 2,000 former Justice Department officials criticised the behaviour of Barr and Trump around the Stone case and said their actions "require Mr Barr to resign".

Barr has been a steady ally of Trump's, clearing the president of the obstruction of justice even when Mueller had pointedly declined to do so, declaring that the FBI's Russia investigation, which resulted in charges against Stone, had been based on a "bogus narrative".