CHICAGO — A huge manhunt was underway after a sheriff’s deputy was gunned down in the city’s northern suburbs early Tuesday.




Lake County, Ill., sheriff’s department spokesman Chris Covelli told USA TODAY that the officer, who was not identified, was killed while he was on a routine patrol in an industrial area in the suburb of Fox Lake shortly before 8 a.m. Tuesday.




The killing marks the fourth incident in nine days where a law enforcement officer has been gunned down while going about his regular duties.




In this latest incident, Covelli said that the officer radioed dispatch shortly before he was shot to say that he was getting ready to check on some suspicious activity he had spotted. He declined to specify what the suspicious activity was.




He then radioed that he was pursuing the suspects by foot, but communication was lost soon after that, Covelli said.




The officer was found in a marshy area, stripped of his gun and other gear, Lake County Undersheriff Raymond Rose told the Chicago Tribune.




Police say they have established a perimeter and are seeking three suspects, one described by law enforcement as a black male and two described as white males.




The manhunt has disrupted service on Metra's Milwaukee District North Line and officials at nearby Grant Community High School said they were ordered by police to keep students inside the school.




"Grant continues to remain in a lockdown situation at the direction of the Fox Lake Police Department,” according to a message posted on the school’s website. "Administrators have gone room to room to ensure all staff and students have been attended to. We will remain in lockdown until we receive direction from the Police Department.”




Covelli said Lake County sheriff's officers were being assisted by several area police departments and federal law enforcement agents as they searched for the suspects.




Twenty-three officers throughout the USA have been killed by gunfire while on duty before Tuesday's incident in Lake County, according to the Office Down Memorial Page.




The incident in the Chicago suburbs comes after a Harris County, Texas sheriff's deputy was gunned down on Friday as he fueled his patrol car.




Police charged Shannon Miles, a suspect with a criminal record and history of mental illness, with capital murder for the killing of Deputy Darren Goforth. Sheriff Ron Hickman described the killing as a "cold-blooded assassination."