Moscow insists that the United States allows Russia's children rights ombudsman Pavel Astakhov to visit a U.S. ranch where troubled adoptees from Russia have been sent, the Russian Foreign Ministry said on Thursday.

“We demand that the American side grants Pavel Astakhov access to the Ranch for Kids private facility to check on the living conditions of Russian children left there by U.S. foster parents,” the ministry’s spokesman Alexander Lukashevich said.

Astakhov visited the respite care home in the U.S. State of Montana in June, but all the children were removed from the facility just before his arrival.

The official said at the time that it had not been made clear whether the children, who are completely isolated from the outside world, receive the necessary help and treatment.

According to Astakhov, the ranch has not kept proper records and ranch head Joyce Sterkel has declined to disclose information on the children to the Russian Embassy officials.

Adoptions have become a thorny issue in U.S.-Russia relations following a series of scandals, including the uproar surrounding a seven-year-old boy who was sent back to Russia unaccompanied in 2010 by an adoptive U.S. mother.

Russian officials claim at least 19 Russian children have died following abuse by American foster parents since adoption of Russian children by Americans began in the early 1990's.