The FBI is currently investigating about 1,000 cases of possible domestic terrorists, the bureau's new chief, Christopher Wray, told Congress.
The investigations pertain to possible white supremacists, white nationalists and people related to environmental movements, according to ABC News.
"[The FBI] has a significant number of agents who are working very, very hard" against domestic terrorism, Wray said in testimony before the Senate Homeland Security Committee.
In 2016, 176 people in the U.S. were arrested on suspicion of links to domestic terrorism, Wray said, according to ABC News.
Discussion over the domestic threat of white supremacists grew after an August clash between white supremacists and counter-protesters in Charlottesville, Virginia, left one woman dead.
Wray told the committee that there is no difference in the way the FBI handles suspected white supremacist terrorism cases and suspected Islamic State terrorism cases.
"We take both of them very, very seriously," Wray said, according to The Hill. "Our focus is on violence and threats of violence against the people of this country. That's our concern -- it's not ideology."
The biggest difference is there is no domestic terrorism charge that can be brought against suspects, Wray said, according to The Washington Post.
"A lot of the [domestic terrorism] cases we bring, we're able to charge under gun charges, explosive charges, all manner of other crimes," Wray said, according to The Hill. "We also work a lot with state and local law enforcement who can sometimes bring straightforward, easy-to-make cases -- homicide cases, things like that."
Wray avoided answering questions on whether a domestic terrorism law should be passed, according to The Post.
Sen. Claire McCaskill, the top-ranking Democrat on the committee, pointed out that the U.S. has seen three times as many attacks committed by white supremacists or anti-government activists than attacks from people connected to international terrorist organizations, according to ABC News.
"[Most people] would assume that the threat from ISIS influence is much greater, and the reality and the facts don't support that," she said.
Wray told the committee that in addition to the 1,000 investigations into suspected domestic terrorists, there are about as many investigations looking at possible "homegrown violent extremists" who might be inspired by groups like ISIS.
People who might have traveled to join ISIS may decide to "stay put" in their own countries following defeats ISIS has suffered in Iraq and Syria, Wray said, according to The Post.
Wray was appointed FBI Director in August, replacing James Comey, who had been fired by President Donald Trump.