Lake County Major Crimes Task Force Cmdr. George Filenko tells WBBM radio that it happened Tuesday morning in Fox Lake, 55 miles north of Chicago.

Sources are telling WBBM that the officer's gun and pepper spray were taken.

The officer, who has not been named, radioed in to dispatch that he was running after three suspects after looking into "suspicious activity," WBBM reported.

Police then lost contact with the officer.

The officer's backup arrived, finding him wounded. The officer died at the scene.

The search has prompted the lockdown of Grant Community High School and disrupted Metra commuter rail service on the Milwaukee District North Line.

Superintendent Christy Sefcik says the school is keeping children and staff away from windows and out of sight. She says school officials were told that police were searching for several "armed individuals."