COEUR d’ALENE — Authorities arrested an 18-year-old Coeur d’Alene man who had allegedly “pledged his allegiance to ISIS” and planned to attack people at local churches using guns, knives and fire, according to the U.S. Attorney’s Office.

Alexander S. Mercurio is charged by federal complaint with attempting to provide material support or resources to a designated foreign terrorist organization.

He was arrested Saturday, according to a news release, the day before he allegedly planned to carry out a “violent plot” in Coeur d’Alene.

Mercurio allegedly planned to carry out a “suicide attack” using “flame-covered weapons, explosives, knives, a machete, a pipe and ultimately firearms,” according to court documents.

“As alleged in the complaint, the defendant swore an oath of loyalty to ISIS and planned to wage

an attack in its name on churches in Coeur d’Alene, Idaho,” Attorney General Merrick B. Garland said in a news release. “Thanks to the investigative efforts of the FBI, the defendant was taken into custody before he could act and he is now charged with attempting to support ISIS’s mission of terror and violence. The Justice Department will continue to relentlessly pursue, disrupt, and hold accountable those who would commit acts of terrorism against the people and interests of the United States.”

The FBI is investigating the case with assistance provided by the Coeur d’Alene Police

Department, the Kootenai County Sheriff’s Office and the Ada County Sheriff’s Office.

If convicted, Mercurio faces a maximum of 20 years in federal prison.

This is a developing story.