US Domestic Terror Probes – Arrests of “racially motivated violent extremists”, including white supremacists, have nearly tripled since 2017, Mr Wray told a Senate committee.
For the first time, Mr Wray called the Capitol attack “domestic terrorism”.
Over 260 people have been arrested in connection with the 6 January storming of the US Capitol to date.
Accepting such behaviour “would make a mockery of our nation’s rule of law” Mr Wray warned during Tuesday’s hearing.
Mr Wray also said the riot may have served as “inspiration to a number of terrorist extremists out there”.
He noted extremists and “bad actors” had mobilised online, using encrypted messaging platforms to evade authorities. “Terrorism today, and we saw it on January 6th, moves at the speed of social media,” Mr Wray said.
The director warned that without a solution to these online issues, “it’s not going to matter how bulletproof the legal process is, or how horrific the crime is, or how heart-breaking the victims are”.
His testimony before the Senate Judiciary Committee on Tuesday marks Mr Wray’s first public appearance since before November’s presidential election.
Mr Wray had not previously spoken publicly about the attack at the US Capitol, although he has worked with local law enforcement and briefed lawmakers in private.
Senators initially focused on questions regarding how the bureau handled a local field office report released the day before the siege that warned of violence in Washington.
The US Capitol Police has said they did not know about the report and received no intelligence from the FBI about the day of the attack.
Mr Wray countered that the report was sent out by the FBI’s joint terrorism task force, discussed at a command post and posted to an online portal that other law enforcement agencies can access.
The director also shot down a theory from some Trump supporters that the Capitol attack was carried out by left-wing agitators in disguise.
“We have not to date seen any evidence of any anarchist violent extremists or people subscribing to antifa [anti-fascist] in connection with the 6th.”
He said the FBI would continue to look for left-wing connections in the ongoing investigations.
Mr Wray also noted that “quite a number” of the extremists investigated thus far belong to far-right anti-government militias.
He said he had “no good answer” about why the field report was not taken more seriously and had not personally seen it until a few days later.