's plea Friday relates to conversations he had with Russia's ambassador last year. He also disclosed that he is cooperating with special counsel Robert Mueller's office.
The plea is the closest Mueller's probe has come to the Oval Office in investigations into the Trump campaign's possible connection to Russian meddling in the 2016 election.
Russian Sen. Franz Klintsevich described Flynn as a scapegoat, according to state news outlet Ria Novosti.
"The former US national security adviser Michael Flynn was just the one they caught. The main object of this attack is of course Donald Trump," Klintsevich is quoted as saying.
Russian Sen. Alexey Pushkov said Flynn's case is much ado about nothing.
"In the United States they continue to inflate a 'sack of smoke ,' " he tweeted. "With Manafort and Papadopoulos, nothing came out. Now they are hyping up the no less empty 'Flynn case. ' "
Former Trump campaign chairman Paul Manafort, who has pleaded not guilty, was indicted in October on charges relating to his undisclosed foreign lobbying on behalf of Ukraine.
George Papadopoulos, a former Trump campaign foreign policy adviser, pleaded guilty in October to making a false statement to the FBI after he lied about his interactions with foreign officials close to the Russian government.
Trump has repeatedly denied any collusion between his 2016 campaign and Russia. Russian President Vladimir Putin has also rejected claims that his country attempted to interfere in the US election.
According to an FBI statement, Flynn communicated with then-Russian ambassador to the US, Sergey Kislyak after being asked by a senior Trump transition official to find out how foreign governments stood on a coming UN Security Council resolution about Israel. The prosecutors did not name any transition officials.
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 details revealed Friday provide the clearest picture yet of coordination between Flynn and other Trump advisers in their contact with Russian officials to influence international policy.
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.
Flynn held the job for less than a month, resigning from the post
after he misled Vice President Mike Pence and then-chief of staff Reince Priebus about his conversations with Kislyak, in which they discussed US sanctions against Russia.
Flynn, 58, is 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.