ORONO — A small fire Friday night at a University of Maine fraternity has been ruled an arson, an official from the state fire marshal’s office said Saturday.

“The cause was intentional human element,” Sgt. Joel Davis of the fire marshal’s office said.

Davis said the fire remains under investigation by fire marshal’s office investigators and local police. No one had been charged in connection with the arson as of Saturday night.

The fire at the Phi Kappa Sigma house on College Avenue began about 11 p.m. and was quickly extinguished by the house’s sprinkler system, Orono fire Lt. Joel Sides said.

He said that fire damage was contained to the attic and that no one was injured.

The fire prompted the evacuation of 15 UMaine students and the temporary closure of College Avenue.

UMaine spokeswoman Margaret Nagle said Saturday that she was told that the fire started in a small mattress on the third floor, which includes some student living space and an attic.

The university offered the displaced students temporary accommodations, assistance that one student accepted, Nagle said. The others found their own places to stay, she said.

Nagle said that the Pine Tree Chapter of the American Red Cross also offered assistance to those who need it.

Nagle said that as of Saturday afternoon, it was not yet clear when the fraternity members would be allowed to return to their house.

Sides said the students likely won’t be allowed to return until the sprinkler system is up and running and electrical service has been restored.