Russian president Vladimir Putin signed into law a controversial bill Friday that bans Americans from adopting Russian children.
The immediate effect of the law prevents 52 children from joining pre-assigned parents in the US.
Americans adopted close to 1,000 Russian children last year, according to U.S. State Department figures. More than 60,000 Russian children have been adopted by Americans over the course of the past 20 years.
The harsh measure was condemned as "politically motivated" by the State Department, and widely viewed as retaliation for U.S. legislation relating to the case of Russian corruption lawyer Sergei Magnitsky.
Magnitsky died in a Russian prison in 2009 after being arrested by the officers he was investigating over fraud. Outcry in the U.S. led to a ban on all officials implicated in the case from travelling to, or holding bank accounts in, the US.
"The Russian government's politically motivated decision will reduce adoption possibilities for children who are now under institutional care," the State Department said in a statement it released Friday.
"We are further concerned about statements that adoptions already underway may be stopped and hope that the Russian government would allow those children who have already met and bonded with their future parent to finish the necessary legal procedures so that they can join their families."
The Russian measure, which will go into effect on January 1, also bars any political activities by nongovernmental organizations receiving funding from the United States, if such activities could affect Russian interests.
It also imposes sanctions against U.S. officials thought to have violated human rights.