Britain, the United States, Germany, France and Italy expressed their support for Georgia's sovereignty. The British Foreign Office said Russia's decision did not contribute to a peaceful settlement in the Caucasus and was out of line with its international commitments.
"We reject this categorically and reaffirm Georgia's sovereignty and territorial integrity," a Foreign Office spokesperson said.
U.S. Secretary of State Condoleezza Rice called Russia's recognition of Abkhazia and South Ossetia "regrettable."
Germany's Angela Merkel said Russia's decision was "totally unacceptable," adding that she hoped the European Union would say the same. France also called the decision "regrettable," while Italy said the move was illegal.
Georgia called the decision to recognize the republics "an unconcealed annexation" and said its ties with Russia would now "stall for a long time, if not for good."
Georgia attacked South Ossetia on August 8 in an attempt to regain control over the separatist republic, which split from Tbilisi in the early 1990s. Most people living in South Ossetia have Russian citizenship and Moscow subsequently launched an operation to "force Georgia to accept peace." The operation was concluded on August 12.
Russia's president signed decrees Tuesday recognizing South Ossetia and Abkhazia as independent states and called on other countries to follow suit.
"This is not an easy decision, but it is the only way to protect people's lives," Dmitry Medvedev said in a televised address a day after both houses of Russia's parliament voted unanimously on resolutions asking the Russian leader to recognize the independence of the two republics following requests from their leaders.
Russian officials have said Georgia lost its right to the two regions following its military offensive against South Ossetia, in which hundreds of people died and thousands were forced to flee the devastated capital, Tskhinvali.
