Donald Trump says he has not asked his attorney general to intervene in the sentencing of his disgraced friend Roger Stone "so far" — but he insists he has the right to do so if he chose.

As the row over alleged political interference in the justice system continued, the president tweeted a quote he attributed to William Barr before adding his own comment: "'The President has never asked me to do anything in a criminal case.' A.G. Barr This doesn't mean that I do not have, as President, the legal right to do so, I do, but I have so far chosen not to!"

His latest comment comes hours after Mr Barr gave an interview to ABC News in which he said Mr Trump's tweets about the case were making it "impossible to do my job".

Prosecutors had recommended a seven-to-nine year sentence for Stone, a former Trump adviser who was convicted last year of offences linked to special counsel Robert Mueller's probe into Russian-back interference in US elections in 2016, including witness tampering and lying to investigators. He is due to be sentenced on 20 February.

However, after the president tweeted his anger at the recommended sentence, the Justice Department, which is headed by Mr Barr, took the unusual step of intervening to suggest a shorter jail term.

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All four of the lead prosecutors in the case immediately resigned, apparently in protest.

With pressure growing on him, amid reports of plummeting morale at the Justice Department, Mr Barr took to the airwaves to insist that he had not bowed to political pressure.

He told ABC News: "I'm not going to be bullied or influenced by anybody ... Whether it's congress, a newspaper editorial board, or the president.

"I'm gonna do what I think is right. And you know – I cannot do my job here at the department with a constant background commentary that undercuts me."

Roger Stone at the launch of his book The Making of the President 2016 in Boca Raton, Florida, in 2017 (Getty)

He added: "I think it's time to stop the tweeting about department of justice criminal cases."

While his apparent criticism of the president, and of his favoured form of commentary on issues close to his heart, could be expected to have sparked a fierce backlash from the White House, Mr Trump was said to be relaxed about it, raising questions over whether he had been forewarned or involved.

But his opponents and chief critics at the capital have accused the president and Mr Barr of blatant abuses of power, with the nation's top prosecutor bowing to pressure from the recently acquitted president emboldened by his allies' refusal to cast a guilty vote for the president's ​abuses of power and subsequent obstruction of the probe investigating his dealings with Ukraine.

House Speaker Nancy Pelosi told reporters this week that Mr Barr has "deeply damaged the rule of law" by facilitating the withdrawal of Stone's recommended sentence and suggesting the move is "Trump's retribution".