* Georgia says Russia sent jets to undermine Rice visit

* Russia says Georgia to blame for wave of violence

* Rice says Georgian sovereignty is 'inviolable'

* Moscow should realise empire is over: U.S. official

By Margarita Antidze and Arshad Mohammed

TBILISI, July 9 (Reuters) - Georgia on Wednesday accused Russia of sending fighter jets into its airspace to undermine a visit by U.S. Secretary of State Condoleezza Rice, who warned Moscow to respect the sovereignty of its pro-Western neighbor.

A U.S. official traveling with Rice to Tbilisi said a simmering confrontation between Georgia and Russia over two breakaway regions could lead to a catastrophe, and that Moscow should realise it is no longer Georgia's imperial master.

Russia made no comment on the allegations it had flown into Georgian airspace. Russia's Foreign Ministry said Tbilisi was stoking tensions in the volatile region by orchestrating acts of violence in the separatist regions.

The two regions -- Abkhazia and South Ossetia -- lie in an arc of land the West sees as a vital route for exporting oil from the Caspian Sea to world markets, and where Washington and Moscow are competing for influence.

Both regions are internationally recognised as part of Georgia but they threw off Tbilisi's control in separatist wars in the 1990s and now run their own affairs with Russian support.

Rice sent a clear warning to Russia before she arrived in Tbilisi, her final stop on a three-day trip that took her to the Czech Republic to sign a missile defense agreement opposed by Moscow and to Sofia to accept a Bulgarian award.

"The United States considers the territorial integrity of Georgia to be inviolable," Rice told reporters in Sofia before arriving in Tbilisi, where she dined with Georgian President Mikheil Saakashvili and was to hold more talks on Thursday.

"There have been a number of moves recently by the Russian Federation that have, in fact, not been helpful in terms of the frozen conflict there with Georgia and Abkhazia," she added, speaking before Georgia accused Russia of violating its airspace.

'EMPIRE IS GONE'

Another senior U.S. official put matters more bluntly.

"Russia needs to realise that the empire is gone. Austria-Hungary is not coming back. The Ottoman empire is not coming back and the Soviet empire is not coming back," the U.S. official, who did not want to be identified, told reporters.

"It's our belief that a military cycle of confrontation will simply develop a momentum of its own and could lead to a catastrophe in the region," he said on board Rice's plane.

Asked what he meant, he said: "A renewed cycle of fighting, which would be horrific."

The deputy commander of Georgia's military, Zurab Pochkua, said four Russian jets had spent a total of 40 minutes in the air over South Ossetia on Tuesday night.

A spokesman for Russia's air force declined to make an immediate comment. Russia has denied allegations in the past that its jets flew into Georgian airspace.

Officials in Tbilisi said Russia was ratcheting up tension because it wanted to sabotage talks they said Rice would hold on new proposals to resolve the separatist conflicts.

"It's a well-known policy of the Russian Federation to arrange provocations to coincide with high-level diplomatic activities," Georgian Foreign Minister Ekaterine Tkeshelashvili told reporters.

Earlier, Russia accused Georgia in the most explicit form to date of being behind attacks this month including a cafe bomb in Abkhazia that killed four people and an exchange of fire in South Ossetia that killed two separatists.

"The actions of Tbilisi present a real threat to peace and security in the South Caucasus and put the region on the edge of a new armed conflict with unpredictable consequences," Russia's Foreign Ministry said in a statement.

Georgia this year accused Russia of trying to annexe the two breakaway regions after Moscow reinforced its peacekeeping troops in Abkhazia and established semi-official ties with the separatists. (Additional reporting by James Kilner and Tatiana Ustinova in Moscow and Niko Mchedlishvili in Tbilisi; writing by Christian Lowe and Arshad Mohammed; Editing by Janet Lawrence)

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