The FBI, focused intently for years on combating terrorism from abroad, is turning more attention to home-grown, U.S. domestic violent extremists, a senior FBI counterterrorism official said on Thursday. It has detected a significant increase in the amount of white supremacist domestic terror cases, according to a report published Thursday.

Arrests related to domestic terrorism in the current fiscal year, which began on Oct. 1, are at 66, exceeding international terrorism arrests, now at 63. Terrorism cases are "the FBI's number one priority," the FBI official said, noting that every one of the bureau's U.S. field offices is affiliated with a local "joint terrorism task force" involving both federal and local law enforcement agencies.

The figures show international terrorism remains a major focus for the FBI, but the bureau is increasingly treating domestic terrorism as an equally important concern. Cases considered domestic terror by the FBI generally include anti-government violence, attacks on racial or religious groups and individuals, as well as anti-abortion and environmental extremism, according to CNN. The internet remains a main source of radicalization for domestic and U.S.-based international terrorists. "Terrorism moves at the speed of the internet," the official said. Given the availability of radical messages in cyberspace, the official said, "homegrown violent extremists" now can become self-radicalized in just months. "Attacks inspire attacks," the official added, noting that attacks such as one against mosques in New Zealand are the type which have inspired by or been copied by other attackers.