The suspect was identified as Dylan Butler, a 17-year-old student at Perry High School, officials said at a news briefing on Thursday.

Responding officers found him dead with an apparent self-inflicted gunshot wound.

Police also discovered an improvised explosive device when searching the high school, Mitch Mortvedt, an assistant director with the state Department of Criminal Investigation, told reporters.

Members of the state fire marshal’s office and the federal Bureau of Alcohol, Tobacco, Firearms and Explosives rendered the device safe.

The shooting occurred on what was to be the first day of the spring semester, according to the school district’s calendar.

Perry, a town of about 7900, is about 65km northwest of Des Moines, the state’s capital city.

The attack took place just after 7.30am, before most students and faculty had entered the building.

Butler was armed with a pump-action shotgun and a handgun, Mortvedt said, and made a number of social media posts around the time of the shooting. The motive for the attack is under investigation.

Four of the wounded victims are students, and the fifth is a school administrator, said Mortvedt, who declined to release any names. Another school district, Easton Valley, issued a statement saying it had received word that Dan Marburger, the high school principal, was shot in the attack.

One victim was in critical condition while the other four were in stable condition.

– AAP