US President Donald Trump is backing a decision by his former national security adviser to seek immunity in congressional investigations of possible ties between his campaign and Russia, but there’s no immediate sign the request would be granted.

Retired General Michael Flynn, who resigned only 24 days after becoming national security adviser, wants protection against “unfair prosecution” if he testifies before the intelligence committees of the US Senate and the House of Representatives, his lawyer, Robert Kelner, said on Thursday.

Testimony from Mr Flynn could help shed light on the conversations he had last year with Sergei Kislyak, Russian ambassador to the United States, while national security adviser for Trump’s presidential campaign.

Mike Flynn should ask for immunity in that this is a witch hunt (excuse for big election loss), by media & Dems, of historic proportion!

— Donald J. Trump (@realDonaldTrump) March 31, 2017

Mr Trump, a Republican, tweeted on Friday: “Mike Flynn should ask for immunity in that this is a witch hunt (excuse for big election loss), by media & Dems, of historic proportion!”

Mr Trump would not comment further when asked about Mr Flynn during a White House meeting with US manufacturers.

White House spokesman Sean Spicer told reporters he was not concerned that Mr Flynn could provide information that could be harmful to the administration.

He said Mr Trump wanted Mr Flynn to testify to “get this matter behind us” but declined to say specifically that he should be granted immunity.

Mr Spicer was quizzed further about Mr Trump’s “long-standing views” on what immunity means, citing comments the President made back in September where he said “if you aren’t guilty of a crime, what do you need immunity for?”.

When asked whether the President thought that Mike Flynn was guilty of a crime, Mr Spicer said “I think he believes that Mike Flynn should go testify.  He thinks that he should go up there and do what he has to do to get the story out”.

US Representative Adam Schiff, ranking Democrat on the House of Representatives intelligence committee, said it was too soon to consider immunity requests.

Mr Schiff said the panel would discuss any request with the Justice Department and the Senate Intelligence Committee, describing such a request “a grave and momentous step”.

A government official with direct knowledge of the case told Reuters that lawyers for Mr Flynn raised the immunity request roughly 10 days ago with representatives of the Senate panel.

The Wall Street Journal reported on Friday that Mr Flynn had also sought immunity from the Federal Bureau of Investigation in exchange for testimony.

Congressional committees and the FBI are also looking into allegations of Russian meddling in the 2016 US election campaign.

Russia has denied allegations that it hacked emails of Democratic groups and released information to tip the presidential election toward Mr Trump.

— with AAP