In a news conference, Chicago Police Superintendent David Brown was quoted as saying by CBS News that a suspect has not yet been identified for the shooting outside Benito Juarez High School in the Pilsen neighborhood.

However, Brown said investigators believe the shooting was "a potential gang conflict."

He told the newspaper an "aggressive" investigation is underway.

A volunteer crossing guard told CBS Chicago that students had just been dismissed when he heard six to eight gunshots at around 2:30 p.m. local time.

The school was placed under lockdown for nearly an hour after the incident.

"Any crime anywhere in the city is obviously a concern to us, but especially, when they're near or around schools. Many of our officers are parents, are uncles, are aunts, of young people," Brown told CBS News. "We are always as police officers extremely concerned of the impact that violence might have on school-aged students."