President Vladimir Putin on Friday signed off on a controversial bill that bans U.S. citizens from adopting Russian orphans.
The U.S. State Department said later in the day that it "deeply regretted" the measure.

Effective from Jan. 1, the ban is part of Russia's lightning response to the Magnitsky Act that President Barack Obama signed earlier this month. The U.S. legislation seeks to punish Russian officials suspected of committing human rights violations.

The Foreign Ministry said on its website Friday that not all Russian orphans have found caring adoptive parents when they crossed the ocean.

"Unfortunately, there is a flip side when our little citizens are adopted by parents of another sort, ending up in desperate situations without any legal protection," the ministry said.

It said at least 19 Russian adoptees had died at the hands of their U.S. parents since 1996, describing the number as the "tip of the iceberg."

No cases of abuse, let alone death, of children adopted from Russia, have been reported in Italy and Spain, which closely follow the United States in terms of the number of such adoptions, the ministry stated.

Russia remains one of the most popular countries for U.S. citizens to adopt. U.S. State Department spokesman Patrick Ventrell said earlier this month that American families welcomed more than 60,000 Russian children into American homes over the past 20 years.

Russian human rights ombudsman Vladimir Lukin slammed the law Friday, saying it ran counter to the Constitution and other Russian laws and could be challenged in court, Interfax reported. He didn't elaborate.

The adoption ban may further tarnish Putin's international standing at a time when the former KGB officer is under scrutiny over what critics say is a crackdown on dissent since he returned to the Kremlin for a six-year third term in May.

"The law will lead to a sharp drop in the reputation of the Kremlin and of Putin personally abroad, and signal a new phase in relations between the United States and Russia," said Lilia Shevtsova, an expert on Putin with the Carnegie Moscow Center, Reuters reported.

"This is only the first harbinger of a chill."