Despite reports of tense stand-offs around the town of Gori and conflicting reports about Russian troop movements, he also said that Russian forces now appeared to be heading back to the separatist enclaves of Abkhazia and South Ossetia as agreed in a French-brokered ceasefire accord.

Meanwhile, American officials in Georgia are investigating reports that Russian forces are deliberately sabotaging Georgian military installations as they withdraw. “When the Russians come across an abandoned Georgian military installation, they are not leaving them as is,” one US official said.

Mr Gates was yesterday ordered by President Bush to organise large-scale humanitarian assistance while Condoleezza Rice, the Secretary of State, spearheads diplomatic efforts to find a durable settlement in Georgia. Dr Rice met President Sarkozy in his Riviera retreat this afternoon and will head to Georgia tomorrow.

The Defence Secretary repeated Mr Bush's warning that Russia's actions in Georgia, where its forces routed their Georgian opponents and took control of the strategic town of Gori and Black Sea port of Poti, would have a lasting effect on bilateral relations with Washington.

“If Russia does not step back from its aggressive posture and actions in Georgia, the US-Russian relationship could be adversely affected for years to come,” Mr Gates said.

But he said that he does not want a return to the Cold War between the two nuclear powers and Russia's actions in the coming days and months will help “determine the future course” of the superpowers’ relationship. He also said there must be “consequences” if Russia does not hold to the ceasefire it has promised.

Mr Gates was asked how he thought the Russians had performed militarily and what their success said about the current state of the Russian armed forces.

He replied: "They clearly had a great advantage in having superior air power and a lot of force that they were able to bring to bear.

"My own view is that - it's a strange thing but since 2004 every August there has been an exchange of fire between the South Ossetians and the Georgians. This year it escalated very quickly and it seemed to me that the Russians were prepared to take advantage of a situation and did so very aggressively."

He said the Russians had gone far beyond what was needed to reaffirm the autonomy of Abkhazia and South Ossetia and wanted to "punish Georgia for rather more than their part in the annual exchange of fire but for daring to try to integrate with the West" and its political and security institutions such as Nato.

He said the Russian military onslaught could also been seen as a "signal to the rest of the former Soviet Union against trying to move out of the Russian sphere of influence".

"They had an opportunity to make some very broad points and I think they seized that opportunity. How they actually performed we will take that analysis at a greater remove, but in terms of what they did rather than how they did it, I think they behaved very badly," he added.