The US State Department has labeled a new ban on adoptions of Russian children by US families "politically motivated."

Russian President Vladimir Putin signed the controversial bill into law on Friday.

The new law, which fully takes effect onJanuary 1, 2013, includes US families that have already begun the adoption process.

"We deeply regret Russia's passage of a law ending inter-country adoptions between the United States and Russia and restricting Russian civil society organizations that work with American partners," State Department spokesman Patrick Ventrell said in a statement Friday.

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

The ban is part of Russia's tit-for-tat response to the US Magnitsky Act, which was signed into law by US President Barack Obama earlier in December 2012.

The act introduces sanctions against Russian officials suspected of human rights abuses and is named after Sergei Magnitsky, a whistleblowing lawyer who died in a Moscow pre-trial detention center in 2009.