Former US President Barack Obama warned then-President-elect Donald Trump not to appoint the disgraced national security adviser Michael Flynn, a former Obama aide says.

Describing reports that General Flynn had misrepresented his contacts with Sergey Kislyak, Russia’s ambassador to the United States, former acting Attorney-General Sally Yates said in a Senate hearing on Tuesday morning (AEST) she was concerned that “the national security adviser essentially could be blackmailed by the Russians”.

The testimony comes amid news President Obama warned then-Mr Trump not to give the post of national security adviser in his administration to General Flynn.

President Obama gave the warning in an Oval Office meeting with Trump just days after the Republican’s surprise election win last November 8.

General Flynn was fired by the Trump administration for lying over his links to Russia.

Responding to the reports, White House spokesman Sean Spicer told a news briefing on Tuesday morning (AEST): “It’s true that the president, President Obama, made it known that he wasn’t exactly a fan of General Flynn’s” during a one-hour meeting with Trump after the election.

An Obama spokesman initially declined to comment.

Mr Flynn has emerged as a central figure in probes into allegations of Russian meddling in the 2016 US election and possible collusion between Mr Trump’s campaign and Moscow.

He had been pushed out by President Obama in 2014 from his job as director of the Defense Intelligence Agency, or DIA, during the Democratic president’s term in office.

Mr Trump fired Flynn, a retired general, in February for failing to disclose talks with Ambassador Sergei Kislyak about US sanctions on Moscow and then misleading Vice-President Mike Pence about the conversations.

Congressional committees began investigating after US intelligence agencies concluded that Russian President Vladimir Putin had ordered hacking of Democratic political groups to try to sway the election toward Trump. Moscow has denied any such meddling.

Mr Trump has also dismissed the allegations, suggesting instead that Mr Obama might have wiretapped Trump Tower in New York or that China may have been behind the cyber attacks.

He has provided no evidence and neither scenario has been supported by intelligence agencies.

Hours before Monday’s Senate hearing, Mr Trump insinuated that Ms Yates, an Obama administration appointment, had leaked information on Mr Flynn to the media.

“Ask Sally Yates, under oath, if she knows how classified information got into the newspapers soon after she explained it to W.H. Council,” Mr Trump wrote on Twitter, apparently mis-spelling the word counsel.

In another Twitter post, Mr Trump noted that General Flynn had been granted top security clearance while working in the Obama administration.

Mr Flynn was fired from the DIA in 2014 for what officials familiar with the issue said was a disruptive management style that included instructing analysts to find intelligence substantiating improbable theories that some subordinates came to call “Flynn facts”.

– AP