Portsmouth Fire Chief Todd Germain says someone set fire to Portsmouth Middle School early Saturday morning.
The call came in around 3:15 a.m.
Sprinklers suppressed the fire until firefighters arrived and extinguished the flames around the main entrance foyer.
Preliminary damage estimates exceed $100,000.
The federal Bureau of Alcohol, Tobacco and Firearms is assisting Portsmouth police and fire officials with the investigation.
Material from The Associated Press was used in this report.
