Former National Security Adviser Michael Flynn pleaded guilty on Friday in federal court to a charge of making false statements to the FBI about his communications with Russia.

Flynn had contacted the Russians at the urging of two top transition officials, according to a court document. Three people familiar with the matter say one of the officials referenced in the document is Jared Kushner, President Donald Trump's son-in-law and senior adviser, and two people familiar with the matter say the other is K.T. McFarland, who served as deputy national security adviser from January to May.

Flynn is the first senior White House official to be charged in the special counsel’s investigation into Moscow’s meddling into the 2016 presidential election, and the first to officially agree to cooperate.

A source close to the White House told NBC News that the Trump administration was "blindsided" by the news of Flynn's plea.

A two-page charging document filed Thursday lists two false statements Flynn made about his interactions with Russian ambassador Sergey Kislyak in late December 2016.

It says Flynn falsely claimed that he had not asked Kislyak on Dec. 29 "to refrain from escalating the situation in response to sanctions that the U.S. had imposed against Russia," and that he didn't recall Kislyak telling him Russia had decided to moderate its response as a result of his request.

Prior to the Dec. 29 call with Kislyak, Flynn called a senior official with the presidential transition team who was with other senior members of the team at Trump's Mar-a-Lago resort in Florida to discuss what to say to the Russian ambassador regarding sanctions, according to the statement of offense. After the call with Kislyak, Flynn spoke with the unidentified member of the transition about the call, including discussion of sanctions.

Two people familiar with the matter told NBC News that K.T. McFarland is the senior official referenced in the statement of offense. McFarland served as deputy national security adviser from January to May, and is now the nominee to be U.S. ambassador to Singapore. Her nomination has not yet been voted on by the full Senate.

Court documents also say Flynn falsely claimed that he didn't ask Kislyak on Dec. 22 to "delay a vote on or defeat" a U.N. Security Council resolution, and then falsely denied that Kislyak had described Russia's response to the request. Before that call, a "very senior member" of the transition team directed Flynn to contact foreign officials, including those from Russia, to learn where they stood and influence the vote, according to the statement of offense.

The "very senior member" was Jared Kushner, three people familiar with the matter told NBC News.

Read the full plea agreement

Read the statement of offense

According to the special counsel's charge, Flynn made the false statements to the FBI on Jan. 24, two days after he was sworn in as national security adviser.

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A source close to President Donald Trump said the developments regarding Flynn are "very, very, very bad."

The concern in the White House is that Flynn, who advised Trump throughout the campaign, will offer up information that could be harmful to the president.

When asked about what Flynn might tell the special counsel, Trump told reporters Saturday from the White House South Lawn that "what has been shown is no collusion, no collusion."

And on whether he's standing by his former national security adviser, Trump added: "We'll see what happens."

The charge to which Flynn pleaded guilty carries a maximum sentence of five years in prison. However, senior federal prosecutors not involved in the case say it is unlikely Flynn will ever spend a day in jail.

Related: Flynn's legal team cuts ties to Trump

The prosecutors said that since Flynn is not being charged with a violent crime, it is likely that government prosecutors would ask for probation and a fine at sentencing. Of course, the federal judge assigned to the case can ultimately impose the maximum sentence and is not bound by the prosecutors' wishes.

Two sources told NBC News that in the Dec. 22 conversation with Kislyak, Flynn asked Russia to either delay or defeat a pending U.N. resolution declaring Israel's settlements in Palestinian territory to be illegal.

The Obama White House and State Department were planning to abstain on the resolution, rather than vetoing it in the Security Council. The Israeli government furiously opposed that abstention, and so did President-elect Trump. No prior administration had failed to veto similar resolutions against Israel, despite opposing its settlements policy. Flynn, while not yet in office, was trying to get the Russians to do what Israel wanted, and thus undercut U.S. policy.

In the Dec. 29 conversation, the sources said, Flynn reassured the Kremlin that the incoming administration, once in office, would reverse the Obama administration's sanctions punishing Russia for its election meddling. At the time, many news organizations reported that it was highly unusual for Putin to refrain from immediately retaliating by expelling American diplomats, in exchange for Obama's expulsion of Russians and the closing of two Russian diplomatic compounds in the U.S.

The following day, Trump tweeted, "Great move on delay (by V. Putin) - I always knew he was very smart!"

Sally Yates, a former acting attorney general, told the Senate in May that she had warned White House lawyers in late January — before she was fired by Trump — that Flynn might be vulnerable to blackmail from the Russians.

Related: Mueller probing pre-election Flynn meeting with pro-Russia congressman

Yates said she had told White House counsel Don McGahn that Flynn had not told the truth to Vice President Mike Pence about his conversations with Kislyak on sanctions.

"To state the obvious, you don’t want your national security adviser compromised with the Russians," Yates told the Senate Judiciary Subcommittee on Crime and Terrorism.

Flynn said in a statement after pleading guilty that he did so "in the best interests of my family and of our country."

"It has been extraordinarily painful to endure these many months of false accusations of 'treason' and other outrageous acts," he said.

"Such false accusations are contrary to everything I have ever done and stood for," Flynn said, noting his more than three decades of military service.

"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. 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."

The White House referred questions about Flynn to outside counsel Ty Cobb, who said Flynn's false statements mirror what caused him to be fired earlier this year.

Related: Manafort and Gates charged with conspiracy in Mueller probe

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

Flynn is the fourth person to be charged in the Mueller probe. Trump's former campaign manager Paul Manafort and his longtime associated Rick Gates were indicted in October on 12 charges, including conspiracy against the U.S. George Papadopoulos, who had been a foreign policy adviser to Trump during the campaign, pleaded guilty to making false statements to the FBI, according to Mueller's office. He entered the guilty plea in Chicago in October.

NBC News reported last month that federal investigators had gathered enough evidence to bring charges in their investigation of President Donald Trump's former national security adviser, according to multiple sources familiar with the investigation.

Flynn, who was fired after just 24 days on the job, was one of the first Trump associates to come under scrutiny in the investigation led by special counsel Robert Mueller into possible collusion between Moscow and the Trump campaign.

Mueller’s investigators have been examining Flynn’s lobbying work, including whether he laundered money, according to three sources familiar with the investigation.

Mueller's team is also examining whether Flynn tried to orchestrate the removal of a chief rival of Turkish President Recep Erdogan from the U.S. to Turkey in exchange for millions of dollars, two officials said.

Flynn's son, Michael G. Flynn, who worked closely with his father, accompanied him during the campaign and briefly worked on the presidential transition, could be indicted separately or at the same time as his father, according to three sources familiar with the investigation.