A bomb exploded on the porch of the Satanic Temple headquarters in Salem, Massachusetts, Monday. No one was in the building when the device landed in the wee hours.

The incident is being investigated by the FBI and Salem Police Department.

The bomb was thrown at around 4:14 a.m., though the remains of the device and the blast damage were not found until 4 p.m.

A Massachusetts State Police bomb squad ensured the explosive was no longer active and used dogs to sweep the area for possible additional bombs, SPD said in a Facebook post.

The bomb caused burn damage to the building’s exterior.

“It was sparking, and there were flames of some type and some scorching on the front of the house,” Lucien Greaves, a co-founder of the Satanic Temple organization, told Boston Fox affiliate WFXT, adding that the incident was a “horrific act of terrorism.”

Mr. Greaves gave a private tour of the headquarters at noon before the bomb and damage were discovered.

“We came in through the back and did the whole tour, and all the while, on the front deck, I guess, was this bomb,” Mr. Greaves told The Boston Globe.

Monday’s attack was not the first time the Salem building was targeted. Earlier this year, a man was arrested and charged in Michigan over plans to attack the building, and another man was arrested and accused of arson at the temple in 2022, SPD said. The temple houses an exhibit on Satanism and witch hunts.

“This year, we’ve gotten a number of threats, a number of bomb threats. About a year and a half ago, we had somebody set fire to the front of the house. There are people who have convinced themselves that we’re involved with some kind of criminal activity,” Mr. Greaves told NBC station WBTS.

Both SPD and the FBI are investigating the bombing.

• Brad Matthews can be reached at bmatthews@washingtontimes.com.