Michael Flynn has admitted lying to authorities over his contacts with the Russian ambassador
US President Donald Trump's former national security adviser, Michael Flynn, has pleaded guilty to lying to the FBI over his links to Russia.
It was alleged that Mr Flynn was dishonest about contacts with Russia's ambassador to the United States, Sergey Kislyak.
When asked in court in Washington whether he wanted to plead guilty, the retired three-star general said: "Yes sir."
A court paper said that Mr Flynn "did wilfully and knowingly make materially false, fictitious, and fraudulent statements and representations."
It added that Mr Flynn "falsely stated and represented to agents of the Federal Bureau of Investigation" his dealings with the Russian ambassador.
The charges relate to events late last year, during the transition period between President Obama and President Trump, when the United States imposed sanctions on Russia and when a United Nations Security Council resolution was pending.
Mr Flynn was interviewed by the FBI just days after Mr Trump's inauguration on 20 January, and was forced to resign in February after White House officials claimed he had misled them about whether he had had discussions with Mr Kislyak.
Mr Flynn was charged under an investigation led by special counsel Robert Mueller and a team of prosecutors.
The investigation is looking into accusations of Russian meddling in last year's presidential election and potential collusion by Mr Trump's campaign.
Mr Flynn has now become the fourth person to be charged in the ongoing investigation.
Charges against three other Trump officials were announced last month.
The three men charged previously are former Trump campaign manager Paul Manafort, his business associate Rick Gates, and former foreign policy adviser George Papadopoulos.
Mr Manafort, who ran the Trump campaign for several months last year, was charged in October with conspiring to launder money, conspiracy against the United States and failing to register as a foreign agent of Ukraine's former pro-Russian government.
Both Mr Manafort and Mr Gates have pleaded not guilty.
Mr Flynn, a retired Army lieutenant general, is the first person who actually worked in the White House to be charged.