United States Secretary of State Condoleezza Rice arrived in the Georgian capital, Tbilisi, on Friday evening to try to broker a peace deal between Russia and Georgia.
Dr Rice will meet Georgian President Mikhail Saakashvili and present him with a formal ceasefire agreement.
She is expected to show strong support for Georgia in the face of Russia's military advance into its territory.
Earlier, the US said its relationship with Russia could be harmed for years because of its "aggressive" actions.
Speaking in Washington, Defence Secretary Robert Gates said Moscow's behaviour had profound security implications, but he stressed he did not see a need for US military intervention.
Meanwhile, President George W Bush again called on Russia to respect Georgia's territorial integrity and honour the EU-brokered ceasefire.
German Chancellor Angela Merkel will also seek a peaceful end to the conflict when she meets Russian President Dmitry Medvedev in the Black Sea resort of Sochi on Friday.
It is thought she will urge Mr Medvedev to adopt a less confrontational approach, and to refrain from questioning Georgia's territorial integrity or undermining the legitimacy of its government.
Dr Rice said it was time for the crisis to be over.
She said that both the US and France strongly backed Georgia's territorial integrity and accused Russia of failing to respect the ceasefire.
"Georgia, whose territorial integrity, independence and sovereignty we fully respect, must be able to go back to normal life," she said.
Meanwhile, there are reports of more Russian troop movements in the west of Georgia.
A Georgian interior ministry official says more than 100 Russian armoured vehicles penetrated deeper into Georgian territory .
Earlier, the ministry said Russian forces were "destroying" the town of Gori.