SALEM, Ore. -

Authorities say an explosive device that went off inside a portable toilet during a softball tournament and injured a woman was likely intended as a prank.

The 40-year-old woman suffered minor injuries when the device went off Saturday at the International School of Beaverton in a Portland suburb.

A short time later a second explosive device went off inside a mailbox just down the road.

Police believe both explosions were intended as pranks and that the devices were made with materials available at grocery stores.

Police evacuated and searched the area. They do not believe the injured woman was intentionally targeted.