Moscow, Feb 22 (IANS/RIA Novosti): Russia's chief investigator has vowed to bring to trial American citizens alleged to have evaded punishment for "serious crimes" against Russian adopted children.

"We intend to prosecute all those US nationals who have not been properly punished for serious crimes against Russian children on US territory," said Alexander Bastrykin, head of the Investigative Committee, an FBI-style law enforcement agency.

He said Russia would place all those people concerned on the international wanted list and seek to have them arrested in absentia by Russian courts.

Russian officials have criticised investigations into the deaths of Russian adoptees in the US and alleged that courts hand down softer punishments for crimes against children from Russia.

Bastrykhin's pledge comes amid a growing row over the death of a three-year-old Russian child in the US.

Russian officials say the boy, Maxim Kuzmin, was murdered by his US adoptive mother in Ector county, Texas.

Russia's child rights ombudsman Pavel Astakhov tweeted that Kuzmin, also known by his US name Max Shatto, had "numerous injuries" and had been given powerful "psychotropic substances" by his adoptive mother.

However, Ector county sheriff Mark Donaldson said he had "no idea where that information came from".

"We don't have any other information right now, until the autopsy report comes in," he said.

Astakhov's accusation whipped up a storm of outrage in Russia, with nationalist politician Vladimir Zhirinovsky, leader of the LDPR party, alleging Americans adopted Russian children to "torment" them, in comments aired on state-run TV.