Sources familiar with the matter told CNN that Trump's son-in-law Jared Kushner is the senior official referred to in the statement of offense.

An attorney for Kushner, now a White House senior adviser, did not comment.

The White House said late Friday morning that "nothing about the guilty plea or the charge implicates anyone other than Mr. Flynn.

"The conclusion of this phase of the special counsel's work demonstrates again that the special counsel is moving with all deliberate speed and clears the way for a prompt and reasonable conclusion," Ty Cobb, a White House lawyer, said in a statement.

In court Friday morning, Flynn's only comments were to answer yes and no to questions from the judge. He told the judge he has not been coerced to plead guilty or been promised a specific sentence. Flynn faces a maximum sentence of five years in prison, according to federal sentencing guidelines, though the judge Friday morning stressed he could impose a harsher or lighter sentence.

In a statement, Flynn said he acknowledged that his actions "were wrong, and, through my faith in God, I am working to set things right.

"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 accept full responsibility for my actions," he said.

Flynn is the fourth person connected to Trump's campaign to be charged as part of Mueller's investigation into possible collusion between the Russian government and members of Trump's team, as well as potential obstruction of justice and financial crimes.

Trump's former campaign chairman Paul Manafort and his deputy Rick Gates were indicted last month; they pleaded not guilty. And Trump campaign foreign policy adviser George Papadopoulos pleaded guilty for making a false statement to the FBI over contacts with officials connected to the Russian government.

Flynn's plea agreement stipulates that he'll cooperate with federal, state or even local investigators in any way Mueller's office might need, according to a document filed in court Friday. He could also be required to participate in covert law enforcement operations (such as wearing a wire) if asked, or share details of his past dealings with the Trump transition and administration.

The agreement adds that Mueller's office won't prosecute Flynn for additional crimes they outlined in his statement of offense Friday, such as his misreported foreign lobbying filings about his work for Turkey. If other prosecutors outside the special counsel's office, such as US attorneys or state law enforcement, wanted to charge Flynn with alleged crimes, they still could, and he's not protected if he lies to investigators again in the future or breaks the terms of his plea agreement.

JUST WATCHED What Trump has said about Michael Flynn Replay More Videos ... MUST WATCH What Trump has said about Michael Flynn 01:33

Calls made during transition

In court, prosecutors detailed calls made by Flynn in late December 2016 to the senior Trump transition team at Mar-a-Lago to discuss conversations with Kislyak. There were multiple conversations with the transition while he was having conversations with Kisyak about Russia sanctions and the Russian response.

According to a statement of offense filed in court, Flynn conducted several calls with senior officials on the Trump transition team about his discussions with Kislyak related to US sanctions of Russia.

Flynn and Trump advisers discussed US sanctions three times. The first call discussed the potential impact on the "incoming administration's foreign policy goals," according to the court filing, from which details were partially read during Flynn's plea hearing.

Flynn then called Kislyak to ask that Russia not respond too harshly to US sanctions, the statement of offense said. He told a Trump transition official about that call. Russia responded by choosing not to retaliate to the sanctions.

KT McFarland was a senior transition official at Mar-a-Lago who was described as discussing with Flynn what, if anything, to communicate to the Russian ambassador about US sanctions, according to sources familiar with the matter. McFarland was not named in the document, but sources confirmed she was one of the transition officials described in the court filings.

An attorney for McFarland declined comment.

McFarland met with Mueller investigators recently to answer questions about Flynn, according to the sources.

According to the special counsel charges, McFarland and Flynn talked about the potential impact of the sanctions on the incoming Trump administration's foreign policy and that the transition team did not want Russia to escalate the situation.

The bulk of the back-and-forth calls from Flynn to the Russian ambassador and to Trump advisers happened around December 29, while the advisers were at Mar-a-Lago in Florida.

They "discussed that the members of the presidential transition team at Mar-a-Lago did not want Russia to escalate the situation," the filing said.

Flynn lied to investigators about these calls with the ambassador, according to his guilty plea and the criminal statement of offense.

The charging document states that Flynn made a false statement to the FBI when he stated that in December 2016 he did not ask Kislyak "to refrain from escalating the situation in response to sanctions that the United States had imposed against Russia that same day; and Flynn did not recall the Russian ambassador subsequently telling him that Russia had chosen to moderate its response to those sanctions as a result of his request."

The document also says that Flynn falsely said he did not ask Kislyak to delay the vote on a pending United Nations Security Council resolution.

Flynn's other instance of lying to investigators involved what he told them about his conversations with foreign officials related to their planned UN Security Council votes on Israeli settlements.

A "very senior member" of Trump's transition team, who sources familiar with the matter told CNN was Kushner, told Flynn on December 22 to contact officials from foreign governments about how they would vote and "to influence those governments to delay the vote or defeat the resolution."

Flynn then asked Kislyak to vote against or delay the resolution, the statement of offense said.

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'This is a win for the White House'

White House allies initially tried to put a positive spin on the news.

One person familiar with the mood in the West Wing insisted top White House officials were breathing a sigh of relief.

"People in the building are very happy," the source said. "This doesn't lead back to Trump in any way, shape or form." The source noted that Flynn is being charged for making false statements, but not for any improper actions during the campaign.

"This is a further indication that there's nothing there," the source said. "This is a win for the White House."

A source with knowledge of the legal team's thinking tells CNN the Flynn plea "is not going to be a problem" for the President, though it could be a problem for people who worked with Flynn. The source said legal exposure for others would depend on what they might have said to the special counsel.

Hillary Clinton, whom Trump defeated in the 2016 general election and was the focus of the "lock her up" chant first popularized by Flynn at the Republican National Convention, declined through a spokesman to comment on Friday's developments.

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Stunning downfall for Flynn

Flynn's lawyers have previously criticized media reports about his connection to the Russia investigation as peddling "unfounded allegations, outrageous claims of treason, and vicious innuendo directed against him." Flynn hasn't spoken publicly since his ouster in February.

The charges mark yet another stunning downfall for Flynn, 58, a retired general who rose to the highest ranks of the Army over a three-decade career -- only to see him fired from the military by the Obama administration before unexpectedly rising again on the heels of Trump's election victory.

A key campaign surrogate and adviser during Trump's presidential campaign, Flynn was tapped as Trump's national security adviser in November 2016, a senior White House job that put him in a vital role for all of the administration's national security and foreign policy decisions.

Though he wasn't initially considered for the top job, Trump's daughter, Ivanka Trump, and son-in-law Jared Kushner made it clear to the Trump transition team that they wanted him there, CNN has reported

Flynn would hold the job less than a month, resigning from the post after he misled Pence and then-chief of staff Reince Priebus about his conversations with Kislyak in which they discussed US sanctions against Russia.

Flynn is also the spark of potential trouble for the President in Mueller's probe, as the special counsel is investigating potential obstruction of justice in the firing of FBI Director James Comey.

Comey testified before the Senate intelligence committee that Trump asked him to drop the Flynn probe during a February Oval Office meeting not long after Flynn resigned as national security adviser.

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Talking about sanctions

Flynn's conversations with Kislyak, which amounted to the crux of his guilty plea Friday, were the main reason for his firing shortly after Trump took office. The calls were captured by routine US eavesdropping targeting the Russian diplomat, CNN has reported.

The Trump transition team acknowledged that Flynn and Kislyak spoke on the day in December 2016 that the Obama administration issued new sanctions against Russia and expelled 35 diplomats, but they insisted the conversation did not include sanctions — including denials that Pence and Priebus later repeated on national television.

Flynn resigned on February 13 after reports that he and Kislyak had spoken about sanctions and that the Justice Department had warned the White House that Flynn was potentially vulnerable to blackmail by the Russians.

Details of how the DOJ warned the White House about Flynn's conduct were revealed months later in stunning testimony from former acting Attorney General Sally Yates, who said that she "believed that General Flynn was compromised with respect to the Russians" because of the misleading denials.

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Warnings before Trump took office

Flynn's legal issues stem from foreign payments he received after he started his own consulting firm.

Flynn founded the Flynn Intel Group after he retired from the military in 2014. The Obama White House pushed him out of his role as head of the Defense Intelligence Agency (DIA), the military's intelligence arm. Flynn was fired over claims he was a poor manager, though he says he was ousted by Obama administration officials unwilling to listen to his warnings about the rise of ISIS and an increasingly aggressive Iran.

Before he was named national security adviser, the FBI began investigating Flynn for secretly working during the presidential campaign as an unregistered lobbyist for Turkey, an investigation he disclosed to the Trump transition team before Trump took office.

Flynn wasn't the only Trump associate who faced scrutiny over foreign lobbying laws -- Manafort also filed a retroactive registration earlier this year for work he previously did in Ukraine.

Federal investigators were probing whether Flynn was secretly paid by the Turkish government as part of its public campaign against Fethullah Gulen, a critic of Turkish President Recep Tayyip Erdogan who lives in exile in Pennsylvania. Erdogan blames Gulen and his supporters for plotting the failed Turkish coup last summer.

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Payments from Russian businesses

Flynn has also been scrutinized for his work with Russian businesses.

In his initial financial disclosure form filed in February with the Office of Government Ethics, Flynn left off payments of thousands of dollars from RT, the Russian government-funded television network and two other Russian companies. Flynn subsequently added the payments in an amended disclosure.

Among the payouts, Flynn received $33,000 of a $45,000 speaking fee for a 2015 speech at a Moscow event hosted by RT, where he sat at the same table as Russian President Vladimir Putin.

Flynn's presence at the gala celebrating RT's 10th anniversary raised eyebrows among his critics. The US intelligence community said earlier this year that the Kremlin uses RT to push propaganda on American audiences, and that the English-language channel was involved in the effort to interfere in the election.

Trump said in May that he hadn't known that Flynn took payments from Russia and Turkey.

Flynn's son also faces scrutiny

Flynn's son, Michael Flynn Jr., has also faced scrutiny from Mueller's investigation, though he was not charged on Friday.

Flynn Jr. served as his father's chief of staff and top aide at their consulting firm, the Flynn Intel Group. In that capacity, Flynn Jr. joined his father on overseas trips, such as Moscow in December 2015 when Flynn dined with Putin at the RT gala.

The younger Flynn has a penchant for spreading conspiracy theories on Twitter. He has smeared Trump's opponents -- ranging from Clinton to Republican Sen. Marco Rubio -- as well as Muslims and other minorities. Most prominently, he peddled the debunked claim that a Washington pizzeria was a front for Democrats to sexually abuse children.

Flynn Jr. has remained defiant as the investigation has heated up. Days after Manafort and Gates were indicted, Flynn Jr. sent a message to his critics: "The disappointment on your faces when I don't go to jail will be worth all your harassment."