The FBI has seen a “significant” rise in domestic terrorism by white supremacists since the fall, a senior bureau counterterrorism official said Thursday.

Arrests of white supremacist terror suspects increased by 40 percent in the past year, the official said, though the FBI would not provide exact statistics to back up the numbers.

The FBI is investigating about 5,000 active terrorism-related incidents in the United States and abroad. About 850 relate to domestic terrorism, while another 1,000 are tied to the Islamic State or affiliated groups.

During the first two quarters of the fiscal year, the FBI made 66 domestic terror-related arrests and 63 international terrorism arrests, according to the official.

The FBI official blamed a rise in copycat and retaliatory plots inspired by a successful attacks as a reason for the increase in attacks by white supremists.

Last month, authorities arrested U.S. Army veteran Mark Steven Domingo, who was accused of planning a massive attack in Long Beach, California, as retribution for the New Zealand mosque shootings that left 51 dead.

President Trump has said the Islamic State has been broken overseas, after years of spreading terror from its base of operations in Iraq and Syria, spurring both coordinated and lone-wolf attacks.

Some analysts had figured terrorism would improve, while others warned of people who left their home countries to fight with the caliphate returning home as trained and motivated terrorists.

The FBI says Islamic State-inspired propaganda is motivating home-grown violent extremists to plot attacks.

The Internet has made it easier for them to recruit disciples, speeding up the time between radicalization and attacks, according to the official.

Read more: Washington Times