Former US acting Attorney General Sally Yates said that she had alerted the White House earlier this year that former National Security Adviser Michael Flynn could be "essentially blackmailed by the Russians", the media reported.
"We believed that General Flynn was compromised with respect to the Russians," CNN quoted Yates on Monday addressing a Senate judiciary panel in a high-profile hearing on Russian meddling into the 2016 Presidential election.
Yates told the panel that she had a meeting with White House Counsel Donald McGahn on January 26 to tell him that she had information that statements by Vice President Mike Pence, based on his conversations with Flynn, were false.
She was joined in the meeting by a senior career official in the Justice Department.
"We weren't the only ones that knew all of this, that the Russians also knew about what General Flynn had done and the Russians also knew that General Flynn had misled the Vice President and others," Yates said, relating the contents of her conversation with McGahn.
The hearing was led by South Carolina's Republican Senator Lindsey Graham. He opened the hearing with an implicit rebuke of President Donald Trump and his alternative explanations for the interference in the election.
Graham said the hacking was not the work of "some 400-pound guy sitting on a bed or any other country", a reference to a comment Trump has previously made on the matter, reports CNN.
Trump fired Flynn, a retired general, for failing to disclose discussions with Russian ambassador Sergey Kislyak about US sanctions against Moscow and for not telling the truth about them to Vice President Pence.
Meanwhile, Yates also warned in her opening testimony that there were some issues she could not address publicly because they involved classified information.
Graham asked Yates whether she had any information about whether there was collusion between members of the Trump campaign and Russia.
"My answer to that question would require me to reveal classified information," Yates replied.
A White House official later told CNN that the administration plans to rebut Yates by employing two strategies: calling into question her objectivity by arguing she is a partisan Democrat and questioning the time-line of events she is expected to present.