Washington, Feb 20 (AFP) Donald Trump's longtime ally Roger Stone was sentenced Thursday to 40 months in prison for impeding a congressional investigation, in a case that ignited a firestorm over the US president's political interference in the justice system.

Stone, a veteran Republican operative and one of Trump's oldest confidants, was convicted in November of lying to Congress, tampering with a witness and obstructing the House investigation into whether the Trump campaign conspired with Russia to cheat in the 2016 election.

"The truth still exists," said US District Court Judge Amy Berman Jackson as she handed down the sentence.

"The truth, still matters. Roger Stone's insistence that it doesn't, his belligerence, his pride in his own lies are a threat to our most fundamental institutions, to the very foundation of our democracy."

Stone was not immediately sent to prison as Jackson said implementation of the sentence would be delayed while she considered his request for a new trial.

Trump sparked a scandal by decrying a "miscarriage of justice" after prosecutors he smeared as corrupt recommended a prison sentence of seven to nine years, in accordance with federal sentencing guidelines.

The president has also taken to Twitter to attack the jurors in the case and Jackson, who last year jailed former Trump campaign chairman Paul Manafort for unlawful lobbying and witness tampering.

Attorney General Bill Barr, who has been blasted for being too close to Trump, personally intervened to have the "extreme and excessive" recommendation withdrawn, prompting all four prosecutors to quit the case.

Trump took to Twitter to praise Barr for getting involved in the "totally out of control" process after a new prosecutor suggested a more lenient sentence of three to four years.

Stone is the sixth aide of Trump -- who was impeached last year for abusing his power but acquitted by the Senate -- to be convicted of charges arising from special counsel Robert Mueller's probe into Russian election interference.

Barr said the president's comments had had no impact on his the decision, but has found himself vilified by Democrats who accuse him and the president of undermining the rule of law.

In addition, more than 2,000 former Justice Department officials have signed a statement calling for Barr to resign.

"A person should not be given special treatment in a criminal prosecution because they are a close political ally of the president," the open letter said.

In a rare public rebuke, Barr -- one of Trump's most staunch defenders -- said the president's Twitter pronouncements in ongoing cases were making his job "impossible." "I think it's time to stop the tweeting about Department of Justice criminal cases," Barr said in an interview with ABC News.

Multiple US media outlets have also reported that Barr has informed the president's inner circle that he might resign if the tweets continue.

His public attempt to distance himself from the president was met with skepticism however by critics who accuse Barr of having repeatedly acting more like the Trump's personal lawyer than a public servant.

Despite his attorney general's warning, Trump continued this week to be vocal in his support for Stone, who appeared in court in a striped suit and a polka-dot tie.

The self-avowed "dirty trickster" was convicted of lying in testimony to Congress about acting as an intermediary between the Trump campaign and WikiLeaks, which released documents hacked by Russia that embarrassed rival Hillary Clinton during the 2016 White House race.

The seven-count indictment also accused Stone of threatening an associate to stop him cooperating with investigators.

Stone accused jury members of being biased against him and appealed to overturn their verdict.

Jackson had previously forbidden Stone from posting on social media about his trial, after he shared a picture of her on Instagram with what appeared to be the crosshairs of a gun sight.

"He was not convicted and is not being sentenced for exercising his first amendment rights, his support of the president's campaign or his policies," the judge said.

"He was not prosecuted, as some have complained, for standing up for the president." Stone, known for his flashy fashion sense, could potentially receive a presidential pardon.

"President Trump could end this travesty in an instant with a pardon, and there are indications tonight that he will do that," news anchor Tucker Carlson said Tuesday in a Fox News segment shared by Trump on Twitter.

The president has already commuted the sentence of nearly a dozen people this week including former Illinois governor Rod Blagojevich, who was jailed for corruption, and a New York police chief imprisoned for tax fraud.

The flurry of clemency actions -- 11 in total -- raised expectations that Trump is considering wielding his power in more controversial cases involving close former associates, including Stone. (AFP)

(This is an unedited and auto-generated story from Syndicated News feed, LatestLY Staff may not have modified or edited the content body)