Michael Flynn pleads guilty of lying to FBI in the Mueller probe.

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 Kislyakin 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.

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.

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.

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.

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.