Vladimir Putin has signed a law banning Americans from adopting Russian children.
The controversial bill is part of a harsh response to a US law targeting Russians deemed to be human rights violators.
Mr Putin signed it less than 24 hours after receiving it from parliament, where both houses passed it overwhelmingly.
The law also calls for closure of non-governmental organisations (NGO) receiving American funding if their activities are classified as political - a broad definition many fear could be used to close any NGO that offends the Kremlin.
It is not immediately clear when the law would take effect, but presidential spokesman Dmitry Peskov was quoted by the Interfax news agency as saying "practically, adoption stops on January 1".
Children's rights ombudsman Pavel Astakhov said 52 children who were in the pipeline for adoption in the US would now remain in Russia.
The bill has angered some Americans and Russians who argue it victimises children to make a political point, cutting off a route out of frequently dismal orphanages for thousands.
"Our unlucky children, our orphans are suffering because they became small change in a political game between two states. This is immoral, this is cannibalism", veteran human rights campaigner Lyudmila Alexeyeva has told the state news agency RIA Novosti.
Vladimir Lukin, head of the Russian Human Rights Commission and a former ambassador to Washington, said he would challenge the law in the Constitutional Court.
US State Department spokesman Patrick Ventrell has expressed regret and urged Russia to "allow those children who have already met and bonded with their future parents to finish the necessary legal procedures so that they can join their families".
Unicef estimates that there are about 740,000 children not in parental custody in Russia while about 18,000 Russians are on the waiting list to adopt a child.
The US is the most common destination for adopted Russian children - more than 60,000 of them have been taken in by Americans over the past two decades.
Mr Putin has also issued an order for the government to develop a programme to provide more support for adopted children.
The law is in response to a measure signed into law by US President Barack Obama this month that calls for sanctions against Russians assessed to be human rights violators.
That stems from the case of Sergei Magnitsky, a Russian lawyer who was arrested after accusing officials of a \$230m (£143m) tax fraud. He was repeatedly denied medical treatment and died in jail in 2009.
Russian rights groups claimed he was severely beaten and accused the Kremlin of failing to prosecute those responsible. A prison doctor who was the only official charged in the case was acquitted by a Moscow court on Friday.
Mr Putin has claimed Russian resentment of the US, funded and encouraged the wave of massive anti-government protests that arose last winter.
The Russian parliament initially considered a relatively similar retaliatory measure, but amendments have expanded it beyond a tit-for-tat response.
Many in Russia have been distressed for years by reports of Russian children dying or suffering abuse at the hands of their American adoptive parents.
The new law was dubbed the Dima Yakovlev Bill after a toddler who died in 2008 when his adopted American father left him in a car in extreme heat for hours.