"[There is a] very strong, growing sense that Russia is not behaving like the kind of international partner that it has said that it wants to be," Condoleezza Rice told a news conference on Wednesday.
"We expect Russia to meet its commitment to cease all military activities in Georgia," she said. She said Washington stood firmly behind Georgia.
"As to choosing, the United States has made very clear that it is standing by the democratically elected government of Georgia," Rice said.
U.S. President George W. Bush said on Wednesday that Rice would travel to Paris to assist European diplomatic efforts, and then onto Tbilisi on August 15 "to demonstrate our solidarity with the Georgian people." She will then report back to Bush at his ranch in Texas on August 16 before returning to Washington on August 17.
Bush also said that Washington would send humanitarian aid to Georgia.
The U.S. secretary of state is expected to meet in Paris with French President Nicolas Sarkozy, who met on Tuesday with his Russian counterpart Dmitry Medvedev in Moscow, eventually working out a plan to resolve the conflict. France currently holds the European Union rotating presidency.
The American president said he hoped that Russia would stick to the plan by stopping all military operations in the region, at the same time expressing his concern over reports that Russian troops were allegedly continuing their advance inside Georgia.
Georgia's Interior Ministry announced on Thursday morning however that Russian troops had begun pulling out of the city of Gori, close to the de facto border with South Ossetia. Russian peacekeepers said on Wednesday that they were removing equipment and weapons from an arms depot discovered near Gori.
Western media reports said on Thursday morning that irregular paramilitary groups tagging behind regular Russian forces had engaged in "looting, burning, murdering and rape" in Georgia.
Russian media earlier reported atrocities by Georgian troops in Tskhinvali, including cases of women and children being "burned alive."
Fighting erupted on August 8 in the volatile South Caucasus region when Georgian forces launched an attack on Tskhinvali, the capital of the breakaway Georgian republic of South Ossetia.
During the subsequent counter operation to expel Georgian troops from the de facto independent republic and to reinforce Russian peacekeepers, Moscow sent some 10,000 troops and several hundred armored vehicles into the area.
Russia has said that at least 1,600 civilians were killed and more than 30,000 fled across the border to Russia following Georgia's military offensive to regain control of the region.
Georgia has reported 60 civilian deaths in the city of Gori. Media sources say that a munitions warehouse was bombed by Russian jets on August 9 and that residential buildings were then hit by subsequent explosions. Russia has strongly denied targeting civilians.
Moscow has meanwhile sent over 1,700 rescue workers and hundreds of medical personnel to the devastated South Ossetian capital, Tskhinvali. Two field hospitals have been set up in the city. Debris is being cleared and measures taken to prevent any outbreak of disease.
South Ossetia and Abkhazia, another breakaway Georgian republic, broke away from Georgia after the collapse of the Soviet Union in 1991. Both republics fought vicious wars with Tbilisi that eventually ended in the retreat of Georgian troops and the regions gaining de facto independence.
When the Rose Revolution street protests swept the pro-Western Saakashvili to power in 2004, the new president immediately vowed to bring the regions back under central government control. Russia had earlier granted citizenship to residents of both republics.
U.S. Republican Party presidential candidate John McCain has also expressed his solidarity with Georgia, telling a crowd in Pennsylvania on Tuesday that, "Today we are all Georgians."