The White House was warned over links between its national security adviser and Russia, US media say.
Michael Flynn is under scrutiny amid reports he spoke to the Russian ambassador to the US about sanctions before Donald Trump’s inauguration.
Associated Press and the Washington Post say the Justice Department alerted the White House over its concerns.
They say the department warned of inconsistencies in what Mr Flynn said about his contact with the ambassador.
It is illegal for private citizens to conduct US diplomacy, and the calls happened late last year, before Mr Flynn was appointed to the administration.
AP said the White House was warned over inconsistencies in his story “weeks ago”. The government and Mr Flynn have not responded to the latest allegations.
Mr Flynn, a retired Army lieutenant general, initially denied having discussed sanctions with the ambassador, and Vice-President Mike Pence publicly denied the allegations on his behalf.
However, Mr Flynn later told the White House they may have been discussed.
The Washington Post said former Acting Attorney General Sally Yates told the White House that their national security adviser “had put himself in a compromising position” by speaking to the Russians before he was allowed, and that the Justice Department had learned he had misled Mr Pence.
Last month, Ms Yates was fired by Mr Trump after refusing to enforce his ban on people from seven Muslim-majority countries.