President Donald Trump's former adviser, Roger Stone, has been convicted on seven charges including obstruction, witness tampering and lying to the US Congress.

Key points: Roger Stone was convicted on one count of obstruction, one count of witness tampering and five counts of lying to Congress

Roger Stone was convicted on one count of obstruction, one count of witness tampering and five counts of lying to Congress Stone worked on Donald Trump's presidential campaign in 2015 and continued as an adviser for some time after that

Stone worked on Donald Trump's presidential campaign in 2015 and continued as an adviser for some time after that Mr Trump said Stone's conviction was an example of an unprecedented "double standard" because his political foes have not been convicted

During the trial, prosecutors pressed their case that Stone lied to members of Congress about reaching out to WikiLeaks — the website that disclosed many hacked Democratic emails ahead of the 2016 US election that proved embarrassing to Democratic opponent Hillary Clinton.

They said he did so to protect Mr Trump from looking bad.

The verdict, in a trial arising from former special counsel Robert Mueller's investigation that detailed extensive Russian interference in that election renews scrutiny on Mr Trump's actions as a candidate, even as he endures an impeachment inquiry that threatens his presidency.

When the verdict was read in the Federal Court and was pronounced guilty, the 67-year-old faced the jury of nine women and three men and showed no outward signs of emotion.

Mr Trump reacted after the conviction of Stone, a long-time friend of his who was once described by then-head of the Democratic National Committee Terry McAuliffe as a "dirty trickster".

"So they now convict Roger Stone of lying and want to jail him for many years to come," Mr Trump wrote on Twitter, asking why his adversaries, including Ms Clinton and Mr Mueller, had not faced the same fate.

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"A double standard like never seen before in the history of our Country?" he wrote.

US District Judge Amy Berman Jackson set a sentencing date of February 6 and rejected a prosecution bid to have Stone jailed until then.

Six of the criminal counts each carry a maximum sentence of five years in prison and the seventh carries a maximum term of 20 years. However, as a first-time non-violent offender Stone is likely to get far less time behind bars.

Stone was one of several former Trump aides to have been charged in Mr Mueller's investigation and one of only two who went to trial rather than plead guilty.

The other was former campaign chairman Paul Manafort, Stone's one-time business partner in a lobbying firm, who was convicted by a jury last year in Virginia of tax and bank fraud and is serving a prison sentence of seven-and-a-half years.

Stone, who has labelled himself an "agent provocateur" and famously has the face of former president Richard Nixon tattooed between his shoulders, was charged with obstructing an investigation, witness tampering and lying to the US House of Representatives' Intelligence Committee five times during its investigation into Russian election interference.

That panel is now leading the impeachment inquiry.

'A good day for the rule of law'

The chair of the Intelligence Committee, Democrat Adam Schiff, labelled the conviction "a good day for the rule of law".

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Chuck Schumer, the top Senate Democrat, said Stone's conviction "sends a powerful and timely message to President Trump and all House and Senate witnesses — past, present, and future — that lying to Congress, witness tampering, and obstruction of Congress are crimes and those who commit crimes do so at their own peril".

Former Trump campaign manager Corey Lewandowski mocked Stone after the verdict, writing on Twitter: "Reunited and it feels so go (sic). Stone and Manafort to re-open new 'consulting' firm behind bars."

Stone and his lawyers, who remain under a court-imposed gag order, had no immediate comment.

Prosecutors also did not comment.

Stone is such a big fan of Richard Nixon that he even has the 37th US president's face tattooed on his back. ( AP: Lynne Sladky )

Opening statements in the colourful trial came on November 6. The trial featured references to the film The Godfather Part II, an impression of Senator Bernie Sanders by a prosecution witness, and testimony by political heavyweights, including former Trump campaign boss Steve Bannon and former deputy campaign chairman Rick Gates.

Those witnesses said they believed Stone had inside information about when WikiLeaks might release more damaging emails about Ms Clinton.

Prosecutors accused Stone of telling politicians five different lies related to WikiLeaks and its founder Julian Assange.

Some of those lies related to the existence of texts or emails. Others pertained to Stone's conversations with Trump campaign officials and a supposed "intermediary" with WikiLeaks in August 2016, whom Stone identified to lawmakers as being comedian Randy Credico.

Reuters