US prosecutors have asked a judge to sentence President Donald Trump's longtime aide Roger Stone to between seven and nine years in jail for lying to Congress and witness tampering.

Stone was found guilty in November on charges related to his efforts to spare the president embarrassment over the probe into Russian interference in the 2016 election.

He was arrested in January 2019 at his home in Florida after the charges were brought by then-special counsel Robert Mueller as part of the Russia investigation.

"When his crimes were revealed... he displayed contempt for this court and the rule of law," prosecutors said in a sentencing memorandum filed Monday.

Prosecutors said Stone's conduct following the start of his trial "demonstrated the low regard in which he held these proceedings."

It cited one instance of him posting an image on Instagram of the presiding judge "with a symbol that appears to be crosshairs next to her head."

Roger Stone, who has a tattoo of Richard Nixon on his back, argued that the charges against him were politically motivated
Roger Stone, who has a tattoo of Richard Nixon on his back, argued that the charges against him were politically motivated AFP / Andrew CABALLERO-REYNOLDS

Stone, 67, had argued that the charges against him were politically motivated, but prosecutors said he lied and bullied witnesses to protect Trump.

When Stone was found guilty, Trump immediately tweeted, suggesting that it was a "double standard like never seen before in the history of our Country."

On Tuesday the US President weighed in again, tweeting: "The real crimes were on the other side, as nothing happens to them. Cannot allow this miscarriage of justice!"

Several US political commentators have suggested Trump may pardon Stone at some time in the future.

Stone began his career as a political aide to Richard Nixon, whose face he has tattooed on his back.

He will be sentenced on February 20.

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