Secretary of State Condoleezza Rice said Friday that Russian forces must leave Georgia immediately after Georgian President Mikhail Saakashvili announced he has signed a cease-fire agreement.
Rice said she had been assured that Russian President Dmitry Medvedev will sign an identical document.
"With this signature by Georgia, this (withdrawal) must take place and take place now," Rice said at a press conference alongside Saakashvili, who said he will "never, ever surrender" in the showdown with Russia.
“Georgia has been attacked. Russian forces need to leave Georgia at once," Rice said. "The world needs to help Georgia maintain its sovereignty, its territorial integrity and its independence.”
Rice said Russia's invasion has "profound implications" for the West. Rice said the time has come "to begin a discussion of the consequences of what Russia has done."
She also noted humanitarian aid already being provided by the United States and other nations and said that access for these supplies "must be immediate and unimpeded."
Rice spoke just hours after President Bush stood outside the Oval Office of the White House and accused Russia of "bullying and intimidation" against Georgia. Bush said the Georgian people had chosen freedom and "we will not cast them aside."
In his weekly radio address, to air Saturday, Bush said, "Russia must act to end this crisis."
Meanwhile, Russian President Dmitry Medvedev said the separatist Georgian regions at the center of the conflict appear destined for independence.
"After what happened, it's unlikely Ossetians and Abkhazians will ever be able to live together with Georgia in one state," he said in a joint news conference in the Russian resort of Sochi with German Chancellor Angela Merkel.
But Medvedev told French President Nicolas Sarkozy by telephone Friday night "that he was also going to sign the accord and that Russia would scrupulously respect its commitments on this agreement, notably confirming the withdrawal of Russian forces," the French leader's office said in a statement.
Rice was in Tbilisi for talks with Saakashvili about details of the cease-fire, which would require Russia to withdraw its combat forces from Georgia but allow Russian peacekeepers to remain in South Ossetia and conduct limited patrols outside the region.
Bush said he would get regular updates from Rice and Secretary of Defense Robert Gates about the continuing showdown between Moscow and Tbilisi over two separatist provinces in Georgia. He voiced firm support for Georgia on Friday.
"Georgia's sovereignty and territorial integrity must be respected," said Bush, speaking just outside the Oval Office before traveling to his Texas ranch for a two-week stay. "Moscow must honor its commitment to withdraw its invading forces from all Georgian territory. ... The people of Georgia have cast their lot with the free world, and we will not cast them aside."
With just five months remaining in his administration, Bush faces one of his biggest foreign policy challenges in dealing with a suddenly assertive Russia, along with unfinished wars in Iraq and Afghanistan and the deeply troubled search for peace in the Middle East. Bush's influence is waning as the world turns its attention to the race to determine who will succeed Bush.
Bush said that Russia, with its air, sea and land attacks in Georgia, had damaged its relations with the United States and other Western powers.
"Bullying and intimidation are not acceptable ways to conduct foreign policy in the 21st century," the president said. "Only Russia can decide whether it will now put itself back on the path of responsible nations or continue to pursue a policy that promises only confrontation and isolation.
"To begin repairing relations with the United States, Europe and other nations and to begin restoring its place in the world, Russia must respect the freedom of its neighbors," Bush said.
Even before the crisis in Georgia, tensions between Washington and Moscow have been rising over disputes such as the independence of Kosovo, NATO's expansion toward Russia's borders and U.S. plans for a missile defense system in Eastern Europe. In another development that infuriated Moscow, the United States and Poland reached a deal Thursday to install a U.S. missile defense base on Polish territory.
Still, Bush said, "The Cold War is over. The days of satellite states and spheres of influence are behind us."
The United States has rushed humanitarian aid to Georgia, using U.S. military planes that put American forces in the midst of the showdown with Moscow.
The president said Americans might be perplexed why the United States had drawn a line in the sand in defense of Georgia, an impoverished country that is largely unknown on the world stage.
"In the years since its gained independence after the Soviet Union's collapse, Georgia's become a courageous democracy," Bush said. "It's people are making the tough choices that are required of free societies. Since the Rose Revolution in 2003, the Georgian people have held free elections, opened up their economy, and built the foundations of a successful democracy."
Aligning itself firmly with Washington, Georgia sent troops to Afghanistan and Iraq. Bush visited Georgia in a show of solidarity and promised that the United States would stand with the former Soviet republic.
Bush acknowledged that Russia is anxious about the spread of democracy to its borders and sees it as a threat to its security.
"The opposite is true," Bush said. "Free and prosperous societies on Russia's borders will advance Russia's interests by serving as sources of stability and economic opportunity."
• Rice Arrives in Georgia With Cease-Fire as Russian Blockade Continues
• Click here to view photos of the conflict in Georgia.
• U.S.: Russia Sabotaging Georgia's Infrastructure During Withdrawal
• Russian Invasion of Georgia Sparks New Cold War Rhetoric
The Associated Press contributed to this report.