LOS ANGELES, May 7 (Xinhua) -- An explosion went off on Wednesday at a middle school in San Diego, south of Los Angeles, school officials said.

    Students at the school about 80 miles (128 kilometers) south of Los Angeles were sent to the playground for their safety as bomb experts swept the campus following the explosion early Wednesday morning.

    Investigators said a boy admitted to placing a homemade device in a trash can at the school, creating a large bang but little damage.

    No one was hurt and there was no major damage at Wagenheim Middle School, spokesman Jack Brandais said.

    Police conducted a search of the campus for other devices, they said.

    The incident comes just three days after a pipe bomb damaged the front of the federal courthouse in downtown San Diego. No one was injured in that incident, which occurred early Sunday and is being investigated by the FBI.