President Donald Trump's ex-national security adviser, Michael Flynn, has been charged with making a false statement to the FBI in January.
Mr Flynn was forced to resign the following month after misleading the White House about meeting the Russian ambassador before Mr Trump took office.
The charges were brought by Special Counsel Robert Mueller, as part of his investigation into alleged Russian meddling in the 2016 US election.
Mr Flynn arrived at court on Friday.
He was expected to plead guilty to one count of knowingly making "false, fictitious and fraudulent statements", reports said. Ahead of Friday morning's court session in Washington DC, two officials were quoted by Reuters news agency as saying he had turned himself in to the FBI.
The former aide is the most senior member of the Trump administration so far to have been indicted by the Mueller investigation.
In October, Mr Trump's former presidential campaign manager, Paul Manafort, was accused of conspiring to defraud the US in his dealings with Ukraine. It also emerged that another ex-aide, George Papadopoulos, had pleaded guilty to making false statements to FBI agents.
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Just over a week ago, US media said his legal team had told the president's lawyers they could no longer discuss the case, prompting suggestions that he had begun co-operating with prosecutors. If confirmed, that would indicate Mr Flynn's lawyers have reached a plea bargain.
According to the charges faced by Michael Flynn, he is accused of:
■ falsely telling FBI agents that on or about 29 December 2016 he did not ask Russia's then ambassador to the US, Sergei Kislyak, to "refrain from escalating the situation in response to sanctions that the United States had imposed against Russia that same day"
■ failing to recall that Mr Kislyak had later told him Russia was moderating its response to the sanctions as a result of his request
■ falsely saying that on or about 22 December 2016 he did not ask Mr Kislyak to "delay the vote on or defeat a pending United Nations Security Council resolution".
IF I HAD UNDERSTOOD THE SITUATION A BIT BETTER I SHOULD HAVE PROBABLY JOINED THE ANARCHISTSGeorge Orwell