The FBI has been classifying the Proud Boys as an extremist group since at least this past summer, according to a law enforcement official in Washington state.
"The FBI categorizes the Proud Boys to be an extremist group with ties to white nationalism," wrote Commander Michael McCabe, author of the document that was completed Aug. 10.
McCabe, who runs internal affairs, training, background investigation and courthouse security for the Clark County Sheriff's Office in Vancouver, Wash., confirmed the document's authenticity to The Guardian in an article published Monday.
He also told the British newspaper that the FBI's classification of the Proud Boys as an extremist group was revealed to him in an Aug. 2 briefing by the FBI.
The FBI said they "have been warning [local law enforcement] for a while" about the Proud Boys, McCabe told The Guardian.
However, in a statement to the Hill, the FBI emphasized its investigations "focus solely on criminal activity of individuals — regardless of group membership—which appears to be intended to intimidate or coerce the civilian population or influence the policy of the government by intimidation or coercion."
The agency also told the Hill "The FBI can never initiate an investigation based solely on an individual’s race, ethnicity, national origin, religion, or the exercise of First Amendment rights."
"Our focus is not on membership in particular groups but on individuals who commit violence and criminal activity that constitutes a federal crime or poses a threat to national security," the statement also said. "The FBI does not and will not police ideology."
Proud Boys founder Gavin McInnes has repeatedly said the group is not a white nationalist or alt-right organization.
Facebook is also banning accounts associated with the Proud Boys.
-- Updated on Nov. 20 at 3:20 p.m.