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WASHINGTON, Aug 19 (Reuters) - The United States warned Georgia against a fight with Russia, a senior U.S. diplomat said on Tuesday as Washington demanded Moscow withdraw its forces more quickly from the former Soviet republic.

“Our message was consistent to our Georgian colleagues ... ‘Avoid a direct military confrontation with Russia at all costs. You cannot prevail. It simply is not possible,’” said Matt Bryza, the State Department diplomat who was sent to Georgia after the crisis erupted.

In some of the most explicit criticism from Washington of Georgia’s actions, Bryza said the United States told Tbilisi that the Georgian military would be no match for Russia.

“Russia is 30 times as big as Georgia, its military is several times as large,” he told reporters.

“It can almost instantaneously roll tanks in. And then even if you succeed miraculously in stopping the tanks, and the infantry, and the mechanized infantry, which move very quickly, it’s the air power that’s finally going to get you. And that is what happened.”

Conflict between Georgia and Russia erupted when Georgia tried to reimpose control over the breakaway, pro-Russian South Ossetia region on Aug. 7-8. Russia responded with a massive counter-attack that overwhelmed Georgian forces.

Russia then moved troops beyond South Ossetia and a second separatist region, Abkhazia, and into Georgian territory.

The United States has condemned Russia’s response, saying Moscow went too far. U.S. officials also voiced frustration for several days that the Russians promised to remove troops under a French-brokered ceasefire deal, but have not done so.

On Tuesday, U.S. officials said they had not seen any serious pullout of Russian forces from Georgia.

“We still don’t see any significant withdrawal of Russian forces out of Georgia,” a senior U.S. defense official said Tuesday evening.

Moscow said it would pull its forces back by Aug. 22 to positions held before the conflict began. A column of Russian tanks and armored vehicles left the Georgian city of Gori on Tuesday.

But Washington demanded faster action.

“We call on them to leave immediately,” State Department spokesman Robert Wood said.

U.S. EQUIPMENT

The senior defense official said it appeared that Russian forces had taken five Humvee U.S. military vehicles that were awaiting shipment out of the Georgian port of Poti after a recent military exercise with Georgian troops.

“Indications are that they have been moved by the Russians,” he said.

But the official played down the significance of the incident, saying he was not aware that it was prompting major interest among senior officials.

The White House said if Russia has seized any U.S. military equipment in Georgia, Moscow must return it at once.

“If the Russians have it, it needs to be returned immediately,” White House spokesman Gordon Johndroe said.

Meanwhile the Treasury Department’s Deputy Secretary Robert Kimmitt said Russia was “not playing by the rules of the 21st century” and causing foreign investors to seek opportunities elsewhere.

The conflict spooked investors and sent Russian stocks tumbling to their lowest levels in nearly two years. It also rattled oil markets because a key pipeline runs through Georgia.

“Their near-term actions ... have done significant damage to Russia’s reputation, both politically and also economically,” Kimmitt told CNBC Television. (Additional reporting by Andrew Gray, Randall Mikkelsen, Toby Zakaria and David Lawder; Editing by David Storey and Jackie Frank)