US President Donald Trump's national security adviser Michael Flynn is struggling to get past a controversy over his contacts with Russian officials before Mr Trump took office
Officials said the conversations have raised concerns within the White House.
Over the weekend, Top White House officials reviewed Mr Flynn's contacts with the Russians and whether he discussed the possibility of lifting US sanctions on Russia once Mr Trump took office, which could potentially be in violation of a law banning private citizens from engaging in foreign policy.
Mr Flynn is a retired US army general and former director of the Defense Intelligence Agency.
An early supporter of Mr Trump, he has been a leading advocate to improve US relations with Russia.
Mr Flynn had initially denied discussing sanctions with the Russians in the weeks before Mr Trump took office on 20 January and Vice President Mike Pence went before the television cameras to repeat the denial and defend Mr Flynn.
When a Washington Post report emerged last week quoting officials saying the subject of sanctions had in fact come up, Mr Flynn left open the possibility that he had discussed sanctions but could not remember with 100% certainty, an administration official said.
A second administration official, also speaking on condition of anonymity, stressed that Mr Pence made his comments based on a conversation with Mr Flynn.
Mr Pence is said to be troubled by the possibility of being misled.
Mr Flynn has apologised to Mr Pence and others over the incident, the first official said.
A third official said the uproar prompted White House chief of staff Reince Priebus to review the matter with other top officials as Mr Trump played host to Japanese Prime Minister Shinzo Abe over the weekend in Florida.
Played golf today with Prime Minister Abe of Japan and @TheBig_Easy, Ernie Els, and had a great time. Japan is very well represented!
— Donald J. Trump (@realDonaldTrump) February 11, 2017
The White House did not respond to a request for comment.
There was no indication from transcripts of Mr Flynn's conversations that he had promised to lift the sanctions but rather he made more general comments about hoping for better US-Russian relations with Mr Trump, the third official said.
Mr Trump has yet to weigh in on the subject, promising to reporters on Friday that he would look into it.
Reporters are expected to ask him about Mr Flynn at a press conference with Canadian Prime Minister Justin Trudeau today.
Mr Trudeau is the third foreign leader received by the Republican billionaire since he took office, following meetings with Britain's Theresa May and Japan's Shinzo Abe.
There was a sense among some officials that while Mr Flynn was on thin ice, he did not appear to be in imminent danger of losing his position, the third official said.
Even so, there were no loud voices speaking up for him.
Mr Trump's senior policy adviser Stephen Miller was asked on NBC's "Meet the Press" yesterday whether Mr Trump had confidence in Mr Flynn.
"It's not for me to tell you what's in the president's mind," Mr Miller said.
Congratulations Stephen Miller- on representing me this morning on the various Sunday morning shows. Great job!
— Donald J. Trump (@realDonaldTrump) February 12, 2017
