Updated

COVINGTON, Louisiana -- Authorities in suburban New Orleans say they have foiled a plot by three teenagers who planned to attack their high school on the opening day of classes.

St. Tammany Parish Sheriff Jack Strain says officials at Lakeshore High School informed deputies July 17 they had uncovered the plot by a group of students that called themselves Day Zero. It wasn't immediately clear how the school found out about the plan.

The sheriff says the 15-year-old boys are being held in juvenile detention on charges of conspiracy to commit terrorism. They turned themselves in this week.

Strain says extra deputies will be at the school when classes start Monday, though authorities believe everyone involved was arrested.

Investigators say the group planned to bring guns and targeted at least one student.