Michael Flynn, the former US national security adviser, has been charged with making false statements in relation to his conversation with the Russian ambassador before US President Donald Trump took office.
He is expected to plead guilty to the charges later on Friday.
The charges stem from an FBI probe into alleged Russia meddling in the 2016 US presidential election.
Flynn, a one-time loyal supporter and aide to Trump, resigned as national security adviser in February after reports surfaced that the Trump administration was warned by the Department of Justice that Flynn’s communication with the Russians could leave the president in a compromised position.
It is illegal for private US citizens to conduct US diplomacy efforts.
According to the court documents, filed on Thursday, Flynn is charged with “willfully and knowingly” making “false, fictitious and fraudulent statements and representations” to the FBI.
When resigning as national security adviser in February, Flynn said he “inadvertently briefed the vice president-elect and others with incomplete information regarding [his] phone calls with the Russian ambassador”.
Flynn had initially told Trump advisers that he did not discuss sanctions with the Russian ambassador, Sergey Kislay.
He later told White House officials that he may have discussed sanctions with Kislay during the transition period.
Flynn is the most senior member of the Trump administration to have been indicted on charges related to the probe, headed by Special Counsel Robert Mueller.
In October, Paul Manafort, Trump’s former campaign manager, and his business associate Rick Gates were charged on 12 count, including conspiracy against the US, money laundering and other financial charges.
Another former Trump-aide, George Papadopoulos, also pleaded guilty to “making false statements to FBI agents”.
There have been no charges specifically related to the Trump campaign.