Federal domestic terrorism investigators are probing “a number of” people animated by “kind of an Antifa ideology,” FBI Director Christopher Wray told lawmakers Thursday.

“We do have a very active domestic terrorism program,” Wray told the House Homeland Security Committee. “And while we're not investigating Antifa as Antifa — that's an ideology and we don't investigate ideologies — we are investigating a number of what we would call anarchist-extremist investigations where we have properly predicated subjects of people who are motivated to commit violent criminal activity on kind of an Antifa ideology.”

Wray stressed that while the FBI has about 1,000 open domestic terror investigations, none of them are focused on "ideology, opinion, or rhetoric," and instead are based on threats.

The extreme left Antifa came to the fore of the national political debate in August, following a string of incidents between the left-wing activists and alt-right white supremacists, or right-wing speakers accused of white supremacy. Those protests and counter-protests culminated in violence at a rally staged by white supremacists in Charlottesville, Va., in which a counter-protester was killed when an individual who attended the rally drove a vehicle into a crowd of left-wing activists.

President Trump was criticized sharply, at the time, for emphasizing that there was violence “on both sides” at the rally, when the murder victim was a member of counter-protesters. The incident also put a spotlight on cases of Antifa threatening violence to stymie speeches by right-wing political figures, ranging from alt-right speakers such as Milo Yiannopoulos to conventional conservatives such as Ben Shapiro.

Mindful of the Charlottesville murder, another lawmaker pressed Trump administration officials about whether counter-terrorism resources are being used to investigate white supremacists, in addition to “ISIS-style terrorists” who have also used vehicles as weapons.

“I believe both of those groups pose equal threats,” Rep. Luis Correa, D-Calif., said during the hearing. “An American citizen that loses her life to a terrorist attack, whether it's motivated by ISIS or its motivated by white supremacists, it doesn't matter its still a tragedy in our society and our country.”

Wray reiterated that the FBI can’t monitor domestic groups as a matter of course the way that it can monitor ISIS and other foreign terrorist organizations.

“In other words, because of the First Amendment issues and the freedom of expression issues and the somewhat ugly history that the FBI has had in the past, we have very specific rules on the domestic terrorism front,” he said. “In order to open an investigation there has to be credible evidence of federal crime, [and] threat of force or violence to further a political or social goal. And if we have all of those three things then we open a very aggressive investigation.”

Homeland Security Secretary Elaine Duke echoed those concerns and said that though her department is also taking steps to curb domestic terrorism.

"One of the major things we’ve done is open the Office of Terrorism Prevention Partnerships, which is making sure every piece of information we get, state and local governments get […] to deal with any types of hate crimes in these groups," she said.