Hours before a US District Judge was to sentence Flynn, Trump appeared to offer support for his former aide.

"Good luck today in court to General Michael Flynn. Will be interesting to see what he has to say, despite tremendous pressure being put on him, about Russian Collusion in our great and, obviously, highly successful political campaign. There was no Collusion!" Trump wrote on Twitter.

Lawyers for Flynn, a retired US army lieutenant general and former insider in Trump's circle, have asked that he be spared jail time after he pleaded guilty to lying to the FBI.

They pointed to the "timely and substantial assistance" he provided to law enforcement in the investigation into Russian interference in the 2016 US presidential election.

Flynn was interviewed 19 times and assisted the team of investigators led by special counsel Robert Mueller that is looking into links between Russia and Trump's campaign and presidential transition team.

Instead of jail time, his lawyers asked for probation of less than a year with minimal supervision and 200 hours of community service.

Mueller's office has also recommended that Flynn be spared jail time.

Flynn pleaded guilty to lying to the FBI about his contacts with Sergei Kislyak, who was then Russian ambassador to the US.

Flynn spoke with Kislyak in December 2016 about US sanctions against Moscow and a vote on a UN resolution on Israeli settlement policy.

Flynn was an early and avid supporter of Trump's presidential campaign, and was named White House national security adviser shortly after Trump's shock election win.

The retired three-star Army general resigned in February 2017 after just 25 days in the position, admitting to having "inadvertently" given "incomplete information" to key people in the White House about his communication with the Russian ambassador.

Australian Associated Press