The evacuation of the Georgian city of Gori began last night, amid fears that Russia would soon advance its troops across the border from the break-away republic of South Ossetia into Georgia itself.

Such an incursion would be a dangerous escalation of a conflict that has already reportedly claimed thousands of lives and displaced tens of thousands more.

Russia -- which said it moved into South Ossetia last week to protect pro-Russians there from "genocide'' by Georgians -- has now been accused of "ethnic cleansing'' itself.

Russia regained total control of Tskhinvali, the South Ossetian capital, yesterday, with Georgia offering a unilateral ceasefire as it withdrew all its troops.

International opinion was hardening against Russia. Moscow has been accused of over-reacting to Georgia's invasion of South Ossetia.

Dangerous

Jim Jeffrey, the US deputy national security adviser, said: "We have made it clear to the Russians that if the disproportionate and dangerous escalation on the Russian side continues, that this will have a significant long-term impact on US-Russian relations.''

American diplomats ruled out military intervention on Georgia's behalf. One US National Security Council official said: "We have no good options. We need Russia's co-operation over Iran and derailing that over a localised conflict in Georgia makes no sense.

"We just have to hope that diplomacy prevails. The next necessary step is for Russia to respond positively to Georgia's ceasefire declaration.''

Sergei Lavrov, the Russian foreign minister, told Condoleezza Rice, the US Secretary of State, that Georgia's president, Mikheil Saakashvili, "must go''. Mr Lavrov said Russia would continue its military action in South Ossetia. He said there was a "continuing direct threat to Russian citizens''.

The few Georgians left in South Ossetia were fleeing from the Russian advance.

In spite of the evacuation of Gori -- a city of around 50,000 people just over the border from the breakaway region -- it seemed last night that Russian troops were for the time being sticking to their side of the border.

However, small arms fire was heard deep inside Georgian territory, suggesting that Russian special forces had made a preliminary advance.

Russian aircraft have already bombed several targets inside Georgia -- including, according to the Georgians, the civilian airport in the capital, Tbilisi.

In addition, Abkhazia, a larger break-away Georgian republic, has become a second front in the battle, with Russian troops reported to be advancing on the Kodori gorge, a foothold of ethnic Georgians in the region.

Ministers in Tbilisi appeared resigned to Russia establishing full control over both Abkhazia and South Ossetia.

Giorgi Baramidze, the Georgian vice prime minister, said: "We won't win a military confrontation. Any face-to-face confrontation has been in Russia's interest. We don't want to do that any more.''

Russia's navy was also involved, deploying a flotilla off Georgia's Black Sea coast. The navy said the ships later put into a Russian Black Sea port, though there were reports that a Georgian boat carrying missile launchers had been sunk.

Mr Saakashvili called on the world to "speak with a united voice, and . . .(say that) Georgia's territorial integrity should be safeguarded''.

There was a rally last night in Tbilisi in support of the government. "We just want to rally our president,'' said one Georgian. "Somehow this has brought us together.''

The US was drafting a UN Security Council resolution condemning the Russian "military assault''. Dr Rice was also planning to send an envoy to mediation talks, which will be brokered by the European Union and the Organisation of Security and Co-operation in Europe (OSCE).

The OSCE is responsible for monitoring the 16-year ceasefire that had prevailed in South Ossetia since it became a semi-autonomous region within Georgia.

Nicolas Sarkozy, the French president, voiced the hope that for a quick end to the conflict following Georgia's retreat.

Vladimir Putin, the Russian prime minister, cut short his visit to the Olympics and flew on Saturday to a field hospital in North Ossetia, which is part of Russia. He denounced what he termed Georgia's "crimes against its own people''. (© Daily Telegraph, London)

- Adrian Blomfield and Damien McElroy in Tbilisi