Former White House national security adviser Michael Flynn pleaded guilty Friday morning after being charged with making false statements to federal officials.

A U.S. government document released by the office of special counsel Robert Mueller said Flynn has been indicted for making “materially false, fictitious and fraudulent statements” to federal officials. He is due in a federal court in Alexandria, Virginia, for a plea agreement hearing at 10:30 a.m. Friday.

Flynn is being charged with misleading federal officials about several conversations he had with then-Russian Ambassador to the United States Sergey Kislyak.

The retired general allegedly misled federal investigators about a Dec. 29, 2016, conversation in which he asked Kislyak to press his superiors in Moscow to “refrain from escalating the situation” after the Obama administration slapped new sanctions on Russia. Flynn also misled the federal officials when he said he did not recall Kislyak later telling him the Kremlin had agreed to do just that.

Watch: Mueller’s Russia Probe Could Last a Year or More

Also cited in the short indictment document are Flynn’s comments to federal officials about a Dec. 22, 2016 conversation with the same senior Russian diplomat. Flynn allegedly made false statements about requesting Russia delay or kill a United Nations Security Council resolution, as well as his recollection of the Russian response.

Then-President-elect Trump tweeted about Russia forcing the Security Council vote to be delayed the day after one of the Flynn-Kislyak conversations.

Great move on delay (by V. Putin) – I always knew he was very smart!

— Donald J. Trump (@realDonaldTrump) December 30, 2016

The retired Army three-star general, who also was fired from his Defense Intelligence Agency director post by the Obama administration, was fired by President Donald Trump after just 24 days on the job. Trump contended he let Flynn go for lying to Vice President Mike Pence; others have said it was due to ongoing Justice Department and congressional investigations of possible ties between Trump’s 2016 campaign and the Kremlin.

Flynn brought to the campaign, then the White House, a list of questionable decisions, many involving his ties to Russian officials as a general-turned-consultant. Flynn served less than 25 days as Trump’s first White House national security adviser before the president claimed he fired him for misleading Pence.

Democrats said Flynn’s indictment proved there was a connection between Trump’s team and Russia.

“This time, the president can’t get away with claiming these charges aren’t about his inner circle’s contacts with Russia, and he can’t dismiss Michael Flynn as some low-level aide,” Democratic National Committee Chair Tim Perez said in a statement. “This development should serve as a clear signal to Republicans in Congress that it is time to take this investigation seriously and stop making excuses for the president’s attempts to interfere with it.”

Flynn is the fourth former Trump campaign or White House officials to be indicted by Mueller, and the first since October. He is the closest individual to Trump to be indicted, having once made it firmly into the president’s inner circle.

Senior White House officials have tried to distance the president from the three other individuals: former Trump campaign chairman Paul Manafort and his top associate, Rick Gates, who were hit with a dozen charges stemming from their private private business practices from 2006 to 2016. Ditto for former campaign adviser George Papadopoulos’s guilty plea on lying to federal officials about contacts he had with well-connected Russians was revealed.

House Democrats have pressed for their Republican counterparts to subpoena the White House for documents they allege will show Flynn’s “egregious conflicts of interest” due to his business dealings with foreign governments. One is Turkey. Another is Russia.

“We believe this paper trail must be pursued to answer the gravest question of all: Did Gen. Flynn seek to change the course of our country’s national security to benefit the same private interests he previously promoted, whether by advising President Trump, interacting with foreign officials, or influencing other members of the Trump administration?” House Oversight ranking member Elijah E. Cummings wrote in a recent letter to panel Chairman Trey Gowdy that featured nearly 20 other Democratic signatures.