Former Trump campaign chairman Paul Manafort could spend nearly two decades in prison on tax and bank fraud charges, prosecutors have said.

The potential sentence stems from Manafort’s conviction last year on eight counts related to an elaborate scheme to conceal from tax authorities the millions of dollars he earned overseas from Ukrainian political consulting.

Court documents filed by special counsel Robert Mueller’s office reveal that Manafort faces possibly the lengthiest prison term in the Russia investigation.

Manafort, who led Donald Trump’s campaign for months during the 2016 presidential campaign, is not charged with any crimes directly related to Russian election interference, the thrust of Mr Mueller’s probe.

But prosecutors have recently revealed that they remain deeply interested in his contacts during and after the campaign with an associate the FBI says has ties to Russian intelligence.

In a 27-page court filing, prosecutors did not recommend a precise sentence for Manafort, but they agreed with a calculation by federal probation officials that his crimes deserve a punishment of between 19.5 and 24.5 years.

They also lay out in great detail for US District Judge T S Ellis III how they say Manafort’s greed drove him to disregard American law.

Trump Russia Probe Manafort
Members of the defense team for Paul Manafort, from left, Richard Westling, Tim Wang and Kevin Downing (Kevin Wolf/AP)

“In the end, Manafort acted for more than a decade as if he were above the law, and deprived the federal government and various financial institutions of millions of dollars,” the prosecutors wrote.

“The sentence here should reflect the seriousness of these crimes, and serve to both deter Manafort and others from engaging in such conduct.”

Manafort has been jailed for months as he awaits his formal sentencing.

His lawyers have said the incarceration has created a mental and physical strain on Manafort, who has recently used a wheelchair in court appearances and will turn 70 in April.

But Mueller’s team made clear that Manafort’s age should not be a consideration, nor does it eliminate the risk that he could still commit new crimes.

“Nothing about the defendant’s age is unusual,” they wrote. “Tax offenders are often older and often, like the defendant, wealthy, but they nonetheless receive substantial terms of incarceration notwithstanding age and health issues.”

Prosecutors often acknowledge mitigating factors that a judge may consider on a defendant’s behalf in favour of a more lenient sentence but none exist here, prosecutors said.

They note that “his pattern of criminal activity” lasted more than a decade, that he conspired to tamper with witnesses despite facing indictments in two different districts and that he repeatedly lied to the government and to a grand jury even after he agreed to cooperate and plead guilty.