"We are not afraid of anything, including the prospect of a Cold War," President Dmitry Medvedev said hours after announcing the Kremlin's decision and one day after Parliament had supported the recognition.
While the risk of a military clash with the West seemed remote, the lack of high-level public diplomacy between the White House and the Kremlin added to an uneasy sense here at least of an escalating crisis.
Medvedev also promised a Russian military response to a U.S. missile defense system in Europe. Washington says the system would counter threats from Iran and North Korea, but Russia says it is aimed at blunting Russian nuclear capability.
The Kremlin's recognition of the breakaway regions of South Ossetia and Abkhazia suggested it was willing to risk nearly two decades of economic, political and diplomatic bonds with its Cold War antagonists.
Medvedev's grim announcement, carried on national television, inspired jubilation on the streets of the rebel capitals. In the South Ossetian capital of Tskhinvali, a parade of cars bearing the South Ossetian and Russian flags blared their horns, women cried for joy and gunmen fired their weapons in the air.
The United States, surprised by the speed of the Russian response, threatened a veto in the U.N. Security Council should Russia ask for international recognition for the territories. "Abkhazia and South Ossetia are a part of the internationally recognized borders of Georgia and it's going to remain so," Secretary of State Condoleezza Rice said. President Bush called the Russian move "irresponsible."
The Kremlin insists, despite some doubts in the West, that its invasion of Georgia was a spur-of-the-moment response to the Georgian military's surprise crackdown on South Ossetia.
By contrast, Moscow has had weeks to weigh the consequences of recognizing the breakaway regions.
As the West focused on Russia's effort to shift Georgia's internationally recognized borders, the Kremlin denounced the U.S. use of a Navy destroyer and Coast Guard cutter named the Dallas to deliver aid to Georgia's Black Sea coast.
"Normally battleships do not deliver aid," Russian Foreign Minister Sergey Lavrov dryly told reporters in English, apparently confusing the word "warship" with "battleship."
Earlier Tuesday, the United States said it intends to deliver humanitarian aid by ship on Wednesday to the beleaguered Georgian port city of Poti, which Russian troops still control through checkpoints on the city's outskirts.
The Kremlin said it accepted the independence claims because the Georgian military assault amounted to "genocide."
But beyond a handful of resolute U.S. foes, such as Cuba and Venezuela, few other nations seem likely to follow the Kremlin's lead.
And the declaration seems to have little practical impact on the lives of people living in the separatist regions, who have lived for years under Russia's economic, political and military umbrella.
Still, the Kremlin recognition marked an initial step toward what could become a push for territorial expansion. Many South Ossetians have expressed a desire for integration into Russia.
The Kremlin's rush to recognize the two regions took Western nations by surprise. Moscow made the move with barely a breather, or dialogue with the West, after the brief war and Russia's pullback from military positions in Georgia late last week.
Medvedev told his nation Georgia had forced Russia's hand.
"Saakashvili chose genocide to fulfill his political plans," Medvedev said. "Georgia chose the least human way to achieve its goal - to absorb South Ossetia by eliminating a whole nation."
Russia's action is likely to send political tremors through Georgia, a Western ally in the Caucasus region, a major transit corridor for energy supplies to Europe and a strategic crossroads close to the Middle East, Iran, Afghanistan and energy-rich Central Asia.
Georgian President Mikhail Saakashvili, a fervent ally of the West, has staked his political career on restoring Georgian sovereignty over its breakaway regions. Georgia's humiliating defeat in its short war with Russia this month could shape the country's politics for years to come.
Georgia's state minister on reintegration, Timur Yakobashvili, told The Associated Press Medvedev's announcement had "no legal status."
Lavrov said recognition was "absolutely unavoidable" for Russia. "Short of losing our dignity as a nation, we couldn't act otherwise," he said.
Alexander Konovalov, president of Moscow's Institute of Strategic Assessment, said that while Medvedev's action was perhaps unavoidable, it was also the result of a chain of missteps by all sides.
He said Saakashvili bore the blame for the devastating attack on Tskhinvali, which triggered the Russian invasion of the small former Soviet republic. "But Russian leaders are guilty too because they kept this conflict warm for many years and tried to use it as a political instrument," he said.
All of the consequences of recognition were not immediately clear, but in the short term Medvedev's announcement seemed to deepen Moscow's isolation.
"This is burning at least one very important bridge," said Masha Lipman, a Russia expert with the Carnegie Moscow Center think tank.
Russian existing membership in the G-8 group of industrial nations may be threatened, as well as its bid for membership in the World Trade Organization.
There are also fears the crisis could spill over into the collaboration between Washington and Moscow on nuclear non-proliferation and cooperation in battling terrorism. Several experts said the declaration limits Russia's room for diplomatic maneuvering.
It undermines the Kremlin's long-standing criticism of the U.S. for acting unilaterally, and it appears to weaken Moscow's rationale for opposing the independence of Kosovo, which formally broke with Serbia in February.
More dangerously, perhaps, recognition for rebel governments in Abkhazia and South Ossetia appears to undercut Russia's rejection, on the grounds of territorial integrity, of the independence claims by separatists in its own turbulent North Caucasus.
Russia will likely argue that South Ossetia and Abkhazia are special cases and that it still regards territorial integrity as crucial principle - an argument unlikely to convince separatists in the North Caucasus.
Associated Press Writers Mansur Mirovalev, Maria Danilova and Steve Gutterman in Moscow; Jim Heintz and Misha Dzhindzhikhashvili in Tbilisi, Georgia; and Yuras Karmanau in Tskhinvali, Georgia contributed to this report.