Russia link probe snowballs as ex-National Security Adviser Michael Flynn admits ...

Former U.S. National Security Adviser Michael Flynn leaves the federal court following his plea hearing in Washington D.C., the United States, on Dec. 1, 2017. (Xinhua/Ting Shen)

Former U.S. National Security Adviser Michael Flynn Friday pleaded guilty to lying to the Federal Bureau of Investigation (FBI) regarding improper contacts with Russian officials, becoming the first member of the President Donald Trump-led administration to be found guilty in the ongoing probe into alleged collusion between Trump's campaign team and Russia.

"My guilty plea and agreement to cooperate with the special counsel's office reflect a decision I made in the best interests of my family and of our country. I will accept full responsibility for my actions," Flynn told a court in Washington, D.C.

"It has been extraordinarily painful to endure these many months of false accusations of 'treason' and other outrageous acts," Flynn, who was fired from his job in February, said in a statement.

"Such false accusations are contrary to everything I have ever done and stood for. But I recognize that the actions I acknowledged in court today were wrong, and, through my faith in God, I am working to set things right," he said.

Special Counsel Robert Mueller's office issued a statement earlier in the day, specifying Flynn's charges and noting he lied to the FBI about his two contacts with Russian officials prior to assuming office.

Flynn had falsely stated that on or about Dec. 29, 2016, he did not ask then Russian ambassador to the United States Sergey Kislyak to "refrain from escalating the situation in response to sanctions" by the United States. He also said he did not remember receiving a call from Kislyak notifying him that Russia has decided to moderate Moscow's response at his request, the statement concluded.

The special counsel's office found that Flynn also falsely stated that on Dec. 22, 2016 he did not ask the Russian ambassador to "delay the vote on or defeat a pending United Nations Security Council resolution," and that he did not remember receiving a subsequent call from the Russian side.

Ty Cobb, a White House attorney, issued a statement following the revelation, saying the White House has also been a victim of Flynn's lies, but downplayed the implications of Flynn's plea.

"The false statements involved mirror the false statements to the White House officials which resulted in his resignation in February this year," Cobb said.

"Nothing about the guilty plea of the charge implicates anyone other than Mr. Flynn," he said.

In October, Mueller's office charged Trump's former campaign manager Paul Manafort, Manafort's deputy Rick Gates, and campaign adviser George Papadopoulos with lying to the FBI. While Manafort and Gates pleaded innocent, Papadopoulos admitted the charges.

Mueller, a former FBI director, was appointed special counsel to probe the alleged collusion between the Trump administration and the Russian government on May 17, 2017 by Deputy Attorney General Rod Rosenstein.

The special counsel's office was set up after former FBI Director James Comey was fired by Trump on May 9. Comey alleged that in conversations prior to the firing, Trump had asked him to drop investigations into Flynn and demanded loyalty.

Flynn, a former U.S. general, was one of the first top brass to support Trump during his campaign. He was picked as the national security adviser after Trump won the election, but was fired on Feb. 13 after allegations of improper contacts with Russia surfaced.