HOUSTON - US authorities on Monday said the death of a three-year-old Russian-born boy was accidental, and that no criminal charges will be filed against his US adoptive parents.

Bobby Bland, the district attorney in Ector County, Texas, said in a statement that his office will not charge Alan and Laura Shatto in the death of Max Alan Shatto, born Maxim Kuzmin.

Max was found dead on January 21 in the backyard of his home in the west Texas's town of Gardendale.

Laura Shatto told the authorities that she found Max unconscious while he was playing with his younger brother Kristopher outside the house. The boy was later pronounced dead at a hospital.

Preliminary autopsy results indicated the toddler body was heavily bruised. However, the final result ruled his death to be accidental.

"There is no evidence to support holding anybody criminally responsible," Bland said, adding that "the tragedy was the result of an accident occurring most likely on playground equipment."

Max and his brother were adopted from an orphanage in northwest Russia last year by the Shattos.

His death sparked outrage in Russia, where the authorities have launched their own investigations and demanded the Shattos face charges.