A teenager has been shot dead while two others are lying critically in hospital following a shooting outside a high school in Des Moines, Iowa, Monday.

Potential suspects have been detained, Sgt. Paul Parizek said, but no charges have been filed as police continue their investigation.

The teens were shot outside East High School, with the gunfire apparently coming from a passing vehicle, police said.

A 15-year-old boy who did not attend the school died and two female students, aged 16 and 18, were in critical condition, police said Monday night.

The incident is at least the 13th shooting at an American campus with K-12 students in 2022, according to a CNN tally.

"Des Moines Police Department detectives continue to investigate this incident. Witnesses are being interviewed, evidence examined, investigative leads followed, and multiple search warrants are being executed," Parizek said.

Police said they started receiving multiple calls reporting gunfire at the school at 2:48 p.m. and found the three victims outside when they arrived. All three were rushed to area hospitals.

East High School Student Kaylie Shannon told CNN affiliate KCCI that she was in a car outside the school when she heard shots.

"I was just sitting in my friend's car and then all of the sudden I heard 11 gunshots and some boys screaming," Shannon said.

The school went under lockdown for more than 40 minutes, but students were dismissed around 3:30 p.m. when police gave an all-clear, according to a statement from Des Moines Public Schools.

Parizek called the incident "a punch in the gut," KCCI reported. "The kids in that school are our community's most precious cargo," he said.

Shooting is 'everyone's worst nightmare'

East High School will be closed Tuesday, the statement from Des Moines Public Schools said.

"The DMPS grief team will be available at East High for students and staff beginning tomorrow through the remainder of the week. School counselors will be available at our other schools for students who need additional support," the district said in a news release.

"I think we can all agree an event like this is everyone's worst nightmare. Tonight, hug your students and love them," Principal Jill Versteeg said in the statement.

Shootings in and near schools have become too common, Superintendent Thomas Ahart said.

"Our staff and students are forced to train for these incidents and the trauma associated with the repeated drills and incidents will remain with them for years to come. It's unfortunate that our state and our country have become a place where firearms are far too easily accessible. We remain committed to protecting our students and staff, but real change to gun laws and access would go a long way to help us," Ahart said in the statement.

The Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) of Kansas City is on scene providing assistance in the investigation, the agency tweeted.

Other agencies assisting with the investigation include the Iowa State Patrol, Polk County Sheriff's Office, the FBI and the Des Moines Public Schools Department of Public Safety.(CNN: Excluding headline)

•File: Multiple agencies are helping with the investigation into the shooting outside East High School in Des Moines

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