Police are investigating after a bomb threat led to the early closure Monday of Portland High School.

Officers say a message was found on the wall of a school bathroom just after 1 pm that mentioned a bomb.

They say the building was thoroughly searched with explosive-detection dogs from both the Portland Police and the Maine State Police.

Officers say no explosives were found, and the threat was determined to be not credible, but the school chose to close early as a precautionary measure.

Investigators are urging anyone with information that might assist in this case to call them at (207) 874-8575.