A six-year-old boy accidentally shot and killed his three-year-old brother while playing “cops and robbers” with a gun their father told investigators he had obtained illegally from a gang member.

Chicago police say the two boys were playing on Saturday evening when the older boy reached on top of the refrigerator and grabbed the loaded hand gun and then accidentally shot Eian Santiago in the face.

The boy was rushed to a hospital, where he died later that night.

• One dead after US zombie shooting
• Curtis Cheng farewelled
• Israel wants more Jews carrying guns

Police subsequently arrested the boys’ father, 25-year-old Michael Santiago, on a felony child endangerment charge.

During a court hearing on Sunday, Assistant State’s Attorney Joseph DiBella said Santiago bought the gun off the street, kept it “wrapped in pyjama pants on top of the refrigerator” and even showed the boy where the gun was.

“He kept the gun for protection because he was a former gang member who snitched on a gang member in a murder trial,” the Chicago Tribune reported DiBella as saying in court.

Santiago had told police about the gun in a videotaped confession, DiBella said.

Judge James Brown set Santiago’s bail at $US75,000 ($A103,360).

Police Superintendent Garry McCarthy said the case tragically illustrates a point he has been making for years about how a major cause of much of Chicago’s violent crime is the flood of illegal guns into the city.

“It’s real simple,” McCarthy said in a telephone interview with The Associated Press on Sunday.

“If that gun is not in the house that kid is alive today. We see this happen over and over and over again.”

McCarthy says his officers routinely seize many times more illegal guns than any city in the nation, including the larger cities of New York and Los Angeles.

The department has seized more than 5500 illegal weapons thus far in 2015.

Chicago also has more homicides than any city in the nation, and the number this year has climbed, with department statistics showing there were 370 homicides as of October 4, compared to 306 for the same period last year.

The number of shooting incidents also has climbed during the same period to 1870 from 1581 last year.