Former US national security adviser Michael Flynn has pleaded guilty to lying to the Federal Bureau of Investigation, prosecutors have said.
Prosecutors added that he had spoken with a top member of US President Donald Trump's transition team regarding his communications with Russia's ambassador to the United States.
Federal prosecutors also said Mr Flynn had been directed by "a very senior member" of Mr Trump's transition team regarding a December 2016 United Nations vote.
Mr Flynn also filed materially false statements and omissions in his 7 March 2017 foreign agent filing over his company's work with the Turkish government, according to prosecutors.
ABC News said Mr Flynn, facing up to five years in jail, was prepared to testify that before taking office Mr Trump had directed him to make contact with Russians.
The White House has said the guilty plea implicates Mr Flynn alone.
"Nothing about the guilty plea or the charge implicates anyone other than Mr Flynn," said Ty Cobb, a White House attorney.
"The false statements involved mirror the false statements to White House officials which resulted in his resignation in February of this year," Mr Cobb said.
He added that the plea "clears the way for a prompt and reasonable conclusion" of the Office of the Special Counsel's probe into Russian meddling in the 2016 US presidential election and potential collusion by Mr Trump's campaign.
Mr Flynn turned himself in to the FBI, two federal law enforcement officials said.
A retired army general who was fired from his White House post in February after revelations he had misled Vice President Mike Pence about his conversations with the Russian ambassador, Mr Flynn is a central figure in the federal investigation led by Special Counsel Robert Mueller.
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The charge against him is another escalation in an investigation that has cast a cloud over the Trump administration since the Republican president took office on 20 January.
In a filing with the US District Court for the District of Columbia, the office said Mr Flynn made false statements to the Federal Bureau of Investigation on 24 January.
Mr Flynn falsely told FBI officials that in December 2016 he did not ask Russia's ambassador to the US to refrain from escalating the situation after Washington had imposed sanctions on Russia, according to the filing.
The sanctions were imposed by outgoing Democratic president Barack Obama.
Mr Flynn, who was a senior adviser to Mr Trump before the president took office, also falsely stated that he did not recall the Russian ambassador telling him that Russia had chosen to moderate its response to US sanctions as a result of his request, the document alleged.
The filing, dated 30 November, also said Mr Flynn falsely stated that he did not ask the Russian ambassador earlier in December to delay a vote or defeat a pending UN Security Council resolution, and that the ambassador never described Russia's response to his request.
Russia has denied a conclusion by US intelligence agencies that it meddled in the election campaign to try to sway the vote in Mr Trump's favour.
Mr Trump has denied any collusion by his campaign.
