President Bush sharply criticised Moscow's harsh military crackdown in the former Soviet republic of Georgia, saying on Monday that the violence is unacceptable and Russia's response is disproportionate.
The United States is waging an all-out campaign to press Russia to halt its retaliation against Georgia for trying to take control of the breakaway province of South Ossetia.
"I've expressed my grave concern about the disproportionate response of Russia and that we strongly condemn the bombing outside of South Ossetia," Bush said in an interview with NBC.
On Sunday, Vice President Dick Cheney said that "Russian aggression must not go unanswered, and that its continuation would have serious consequences for its relations with the United States."
Russia battled Georgian forces on land and sea, reports said late on Sunday, despite a Georgian cease-fire offer and its claim to be withdrawing from South Ossetia.
US officials said Moscow was only broadening its retaliation against Georgia for trying to take control of the region.
The sheer scope of Russia's military response has the Bush administration deeply worried. Russia on Sunday expanded its bombing blitz in areas of Georgia not central to the fighting.
Cheney spoke on Sunday afternoon with Georgian President Mikhail Saakashvili, Cheney press secretary Lee Ann McBride said. "The vice president expressed the United States' solidarity with the Georgian people and their democratically elected government in the face of this threat to Georgia's sovereignty and territorial integrity," McBride said.