COEUR d’ALENE — The 18-year-old Coeur d’Alene resident accused of planning to attack local churches on behalf of ISIS pleaded not guilty in federal court Wednesday morning.

Alexander S. Mercurio is charged with attempting to provide material support to a designated foreign terror organization. If convicted, he faces a maximum penalty of 20 years in prison and up to a lifetime of supervised release.

Federal authorities arrested Mercurio Saturday, the day before federal prosecutors believe he planned to attack people attending a church near his home in Coeur d’Alene. He allegedly planned to incapacitate people by beating them with a metal pipe, “slit their throats with a knife or a machete” and then start fires inside the church.

Mercurio allegedly told confidential sources he planned to “carry out a martyrdom operation” in Coeur d’Alene April 7, according to court records. Just before doing so, he said he wanted to donate “every last cent” in his bank to ISIS, a sum of around $11,000.

Mercurio waived his right to a detention hearing Wednesday. He will remain in custody while a trial in the matter is pending.

A jury trial is scheduled to begin May 28. Proceedings will remain in Coeur d’Alene.