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U.S. officials assailed Russian President Vladimir Putin on Friday after he signed a bill banning American families from adopting Russian children, with Sen. John McCain calling the law "shameful."

The harsh law was seen as retaliation for an American law that calls for sanctions against Russians deemed to be human rights violators.

But U.S. officials said the two laws are hardly comparable. McCain, R-Ariz., said the idea that banning all adoptions to America is a fair tit-for-tat is "utterly baseless."

"Our law singles out and punishes individual Russian officials who are corrupt and complicit in gross human rights abuses," McCain said in a statement Friday. "Russia's barring of adoptions broadly punishes the neediest, most defenseless, and most innocent members of its own society."

He called it "shameful and appalling" that Putin signed a bill that effectively denies thousands of Russian children a loving home.

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    The law cuts off one of the main international routes for Russian children to leave often dismal orphanages. Russia is the single biggest source of adopted children in the U.S., with more than 60,000 Russian children being taken in by Americans over the past two decades.

    The State Department, stressing how many children had been taken in by American parents, said Friday that they "deeply regret" the law's passage.

    "The Russian government's politically motivated decision will reduce adoption possibilities for children who are now under institutional care," spokesman Patrick Ventrell said.

    Ventrell went on to express concerns about statement that adoptions "already underway" could be halted. He urged the Russian government 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."

    U.S. Ambassador to Russia Michael McFaul also said last week that the bill would "link the fate of orphaned children to unrelated political issues."

    He noted that the two nations had already struck an agreement to improve safeguards to protect adopted Russian children, and said "it is unfortunate that now the Duma has apparently decided to take away these negotiated safeguards and ignore the hard work and negotiations on both sides that went into putting this agreement together."

    Putin said U.S. authorities routinely let Americans suspected of violence toward Russian adoptees go unpunished -- a clear reference to Dima Yakovlev, a Russian toddler for whom the bill is named. The child was adopted by Americans and then died in 2008 after his father left him in a car in broiling heat for hours. The father was found not guilty of involuntary manslaughter.

    UNICEF estimates that there are about 740,000 children without parental custody in Russia, while only 18,000 Russians are now waiting to adopt a child. American adoption advocates say the move sentences untold numbers of Russian kids to a childhood without loving parents.

    The Associated Press contributed to this report