WASHINGTON (AFP) - Top White House aide Michael Flynn was on the hot seat Monday, his job apparently on the line over disclosures he may have misled Vice President Mike Pence about his discussions with Russia's ambassador.

President Donald Trump has so far been uncharacteristically silent on Flynn's fate, fuelling speculation about whether his national security advisor can survive the latest controversy.

"Really that's a question for the president," said Sebastian Gorka, the president's deputy assistant on national security, when asked about it on NPR radio early Monday (Feb 13).

At issue is Flynn's changing account of his discussions with Ambassador Sergey Kislyak in December, weeks before Trump took office and as the Obama administration was about to retaliate for Moscow's meddling in the US elections with additional sanctions.

After the contacts first came to light in January, Flynn denied the issue of sanctions had been discussed.

On Jan 15, Pence went on US television talks shows to say Flynn had told him that the sanctions had not come up in the conversations with Kislyak.

But on Friday, the Washington Post, citing current and former senior administration officials, reported that US intelligence had monitored the conversations and that Flynn had signalled to Kislyak not to overreact to the sanctions, that the Trump administration would be in a position to review them.

Flynn, after first denying sanctions had been discussed, said through a spokesman he could not recall whether they had come up in his talks with Kislyak.

A White House official told media that Pence's comments "were based on his conversation with General Flynn".

On Sunday, White House Senior Policy Adviser Stephen Miller, asked on NBC's Meet the Press if Trump has confidence in Flynn, answered: "That's a question that I think you should ask the president." .

Adam Schiff, the senior Democrat on the House Intelligence Committee, called the allegations "staggering," saying Monday that if they are true, Flynn should resign or be fired.

"Either he was lying about not having discussed that, or he forgot," said Democratic Senator Al Franken on CNN's "State of The Union" program Sunday.

"I don't think you want a guy in either of those scenarios to be in that position" as White House national security advisor, he said.

The issue comes up just days before Trump has his first official talks with Israeli Prime Minister Benjamin Netanyahu, talks in which the president's national security advisor would normally have a key role.

Flynn, a retired army three-star general and former head of the Defence Intelligence Agency, has been a close advisor to Trump since early in his campaign for president.

But his choice as Trump's top national security advisor has been controversial. Many in the US intelligence community say he is ill-suited for the crucial job; they note he was fired as DIA chief after two years for alleged poor management.

He sees militant Islam as the biggest threat to global stability, and has said that Washington and Moscow need to cooperate on the issue.

The Justice Department and Congress are both investigating possible links between Trump campaign advisors and Moscow, and have concluded that Russian President Vladimir Putin personally directed an operation to interfere in the US election.

On Dec 29, the Obama administration sanctioned four Russian individuals and five entities, and expelled 35 Russian diplomats in retaliation.