A US court has agreed to delay the sentencing of Donald Trump's former national security adviser for lying to the FBI.

Michael Flynn, a former general, admitted last year that he was not truthful when he discussed contact with the then Russian ambassador to the US, Sergei Kislyak.

Mr Flynn was interviewed by the FBI just days after Mr Trump's inauguration on 20 January, and was forced to resign in February after White House officials claimed he had misled them about whether he had had discussions with Mr Kislyak.

At today's hearing a judge told Flynn: "Arguably, you sold your country out.

"Arguably, this undermines everything this flag over here stands for."

District Judge Emmet Sullivan insisted that it was a "very serious offence".

Judge Sullivan said he could not "hide my disgust, my disdain" for the crime, but later clarified that he was "not suggesting" Flynn committed treason.

Amid a warning of possible jail time, the judge offered Flynn the option of delaying the sentence until he completes a cooperation agreement with federal prosecutors - an offer the former national security adviser accepted.

US special counsel Robert Mueller, who is heading the probe into alleged interference in the 2016 election, had recommended Flynn should not serve prison time because of his "substantial" co-operation with the investigation.

The judge did not set a new date for sentencing but asked for a status report by March 13.

Tweeting ahead of today's hearing, President Trump wished Flynn luck - claiming his former aide was being put under "tremendous pressure".

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!

— Donald J. Trump (@realDonaldTrump) December 18, 2018