A senior Russian diplomat said Tuesday that the United States remains the most problematic country for orphans adopted from Russia.

Speaking at the 3rd Russia-US Child Protection forum, Konstantin Dolgov, the foreign ministry's envoy for democracy, human rights and supremacy of law, said US authorities should pay thorough attention to the so-called rehoming of adopted children via Internet ad boards. He added they should conduct an "investigation of the facts of grave violations of children rights."

Earlier this month, Reuters reported that at least 26 Russian children were "exchanged" by their US foster families with other adoptive parents via the Internet. Moscow said many children were given to pedophiles and makers of child pornography via these exchanges.

The 18-month journalistic investigation revealed that the transfers, beginning on online bulletin boards, led to cases of child abuse and neglect, and were carried out in a largely unregulated environment.

Dolgov said that many US foster families adopted children only to become eligible for social security payments and tax deduction.

He reiterated Moscow's demands that the US authorities should inform Russia of all cases of child abuse and allow Russian diplomats unrestricted access to the information.

Dolgov also demanded a reinvestigation into the death of Maxim Kuzmin, a Russian boy who died three months after being adopted by a US couple, and into the alleged abuse of several other adopted children, adding that both investigations should involve Russian representatives.

The two-day forum is being held in the Siberian city of Khanty-Mansiysk, with over 250 experts and officials participating.

Two previous Child Protection and Welfare forums took place in the Russian republic of Buryatia in 2011, and in America's Chicago in 2012.