LOS ANGELES - An 11-year-old American boy fatally shot his grandmother and then himself after being asked to clean his room in southwestern US state of Arizona, local news media reported on Monday.

The boy had been asked by his grandparent Doyle Hebert and Yvonne Woodard throughout the day on Saturday to clean his room since he wouldn't do it at their home in Litchfield Park, Maricopa County Sheriff's Office Sgt. Joaquin Enriquez was quoted as saying by CBS affiliate KPHO-TV.

While the couple was watching television, the boy came up behind them and shot Woodard, his grandmother, in the back of the head just after 5 pm local time with a handgun which belonged to his grandfather. Then the boy turned the handgun on himself, KPHO-TV reported.

The old couple had full custody of the boy whose identity has not been revealed by police.

The boy was only confirmed a student of the Western Sky Middle School in a statement released by the Litchfield Elementary School District on Monday.

"We are heartbroken to learn of the tragic death of one of our students and his grandmother. They were valued members of our Wildcat family at Western Sky Middle School and will be deeply missed," said the statement.

"Our hearts are with the Hebert family and their loved ones as they endure this unimaginable pain," the statement added.

Maricopa County Sheriff's Office said the investigation is still ongoing.