The United States says it "deeply regrets" the approval by Russian President Vladimir Putin of legislation that bans adoptions
of Russian children by U.S. citizens.
U.S. adoption advocacy groups and rights NGOs also slammed the move, which has stunned hundreds of U.S. families in the adoption process.
In a statement, State Department spokesman Patrick Ventrell called the Russian move "politically motivated" and said the United States hoped adoption cases already under way would not be affected.
The State Department also expressed concern at another provision of the Russian legislation, which bars people who hold U.S. citizenship from being a member or officer of any nonprofit organization "participating in political activities in the Russian Federation."
It also includes sanctions against Americans who allegedly committed crimes against Russian citizens or are determined to have been involved in "the violation of fundamental human rights and freedoms."
U.S., Russian, and international adoption-advocacy groups and human rights NGOs have slammed the legislation.
Lauren Koch, a spokeswoman for the National Council for Adoption (NCFA) in the United States, described the Russian move as "a great tragedy."
"At this point all we can hope for is that President Putin will honor the terms of the original [U.S.-Russian] bilateral agreement [on adoption that entered into force] in November and, at a very minimum, allow those children that have been matched with a family to come to America and join their families," Koch said.
"NCFA and orphan advocates from all around the world -- we plan to renew our efforts and continue to be the voice for these children until their right to be loved, protected, and secure in a family is realized."
U.S. rights watchdog Freedom House called the law "immoral."
Freedom House President David Kramer said in a statement, "Rather than addressing the grave and widespread human rights abuses which occur frequently in Russia, this legislation harms Russian children and destructively singles out Russian NGOs."
On U.S. adoption-website forums, would-be adoptive parents said they were "stunned" and "devastated."
Russian opposition figures have called for a demonstration on January 13 that would demand the dissolution of the legislature and the repeal of the legislation.
It was introduced in reaction to a U.S. law known as the Magnitsky Act. That law imposes sanctions on Russian officials linked to the death of whistle-blowing lawyer Sergei Magnitsky in a Moscow jail in 2009 and other alleged human rights abuses.
The new law goes into effect on January 1.
The United Nations estimates there are some 740,000 Russian children without parental custody. Over the last 20 years, about 60,000 Russian children have been adopted by Americans.
With reporting by RFE/RL correspondent Richard Solash, RIA Novosti, and Interfax